If you run a 13.5 or 10.5 in your CAT2k, then it will be fine. I have a 10.5 in mine and haven't snapped any of the plastic universals at the dogbone. The real problem with those universals is the cup end where the wheel axle mounts into with pins. The holes in that cup do not have a lot of surrounding material, and they can snap if you put too much power through them. I've snapped two so far, but have otherwise had no problems.
Long story short, if you're not an idiot with your motor selection, then the drivetrain on any of these vintage 4wd buggies will be just fine.
I have experience running the following, listed in order of ranking by my personal preference (last is best):
Lazer ZXR: Not as much droop as the CAT2k or YZ10, so the jumping performance is relatively poor. I really want to put more time into mine, to play around more with setup, but in short, it has very quick steering. The main advantage over the CAT and YZ10 is the adjustable center one-way. Great for low grip tracks and/or hairpins. Weaknesses include the steering rack, C-hubs, and front shock tower mount. Center one-way locking nut tends to back out, so check that after every run. The ZXR body fits rather tight, so you may find yourself having to run the ZX body to fit the electronics comfortably.
https://www.youtube.com/watch?v=xdqh07syntM
YZ10 870C: Fantastic on loose dirt. Needs some custom work to increase front droop, and additional tuning with the springs/pistons/oil, especially at the rear. Has a tendency to nose-dive off of jumps, owing to the rear bottoming out on the jump face. Weaknesses include magnesium bulkheads (easily replaced with YR4 plastic units) and magnesium steering blocks and rear hubs (haven't broken one yet, knock on wood). Also watch out for the steering rack. They tend to break on the bottom part of the servo saver side. Get a YR4 aluminum one if you can find it.
https://www.youtube.com/watch?v=w9jBQuxy9xQ
https://www.youtube.com/watch?v=KUtnloOaBLE
YZ10 '93 Works: Ultimate version of the 870C. Wider arms and countermeasures to deal with suspension and steering slop. I've yet to drive it on a loose dirt track, but I suspect it would perform better than the 870C. On medium to high grip, hard-packed dirt, it handles very nicely, but makes its weight known. It is heavier than the 870C, owing to the extra parts and the aluminum bulkheads. Rear bulkhead is adjustable for belt tension, but this also means it can move around a bit, even when tightened down. Check this after reach run. Extremely rare, but I really love this car. It is as fast as it looks.
https://www.youtube.com/watch?v=PLOffnbzhuU
https://www.youtube.com/watch?v=VAfXmYW3iw4
https://www.youtube.com/watch?v=nsayupdV7po
CAT2k: The original 2000 and the 2000EC are basically the same car, with the main difference being stand-up vs. lay-down shocks. The former is generally better on loose/rutted surfaces, while the latter is generally better on carpet or astro. Extremely competent chassis and among the most tunable of all of the vintage 4wd buggies. Clicker-type center one-way is in between the full one-way that the YZ10s have and the almost fully locked one-way on the Lazer. Arguably an over-complicated design makes it difficult to work on. Steering knuckles are not very strong. Center pulley that drives the rear belt does wear down and lead to belt skipping. I like that it can be replaced without replacing the entire slipper hub (unlike the YZ10), but do watch out for this.
https://www.youtube.com/watch?v=Hq2CsTu4ptA
https://www.youtube.com/watch?v=3uAVjM4uOHo
https://www.youtube.com/watch?v=edzncixXuX4
'94 YZ10: As fast as the CAT2k in the right hands, with the right setup, but simpler design, easier to work on, and far stronger. The center one-way takes a bit of work to get used to, or you can play games with it to slow it down (e.g., run plastic bushings in the pulley instead of bearings...anything to add friction and slow it down). Drives like a B44 with belt drive, in my view. The only thing I've really broken on this car is the upper tie rod. It's a tiny 16mm (or 20mm...can't remember) long unit, and can bend or break easily. The rest of it is damn near bullet proof, and not particularly heavy, despite that fact. Easily my favorite vintage 4wd runner.
https://www.youtube.com/watch?v=Kw38kg44k90
https://www.youtube.com/watch?v=4vfbdqCf1Ws
https://www.youtube.com/watch?v=dqox7DbIPsM
https://www.youtube.com/watch?v=9JZGmUma24E
Others to consider:
Losi XX4: Many consider this the best among the vintage 4wd buggies, but I personally beg to differ. Firstly, it is not as "vintage" as the other vintage buggies, so in some vintage races, it would not even be legal. Second, and most importantly, it is quite fragile. This is very important to consider, since more often than not, you'll be on the track with a bunch of bozos banging into you left and right (at least that's been my experience at vintage races, since a lot of them only race a few times per year, at most). Almost everyone I've known with a XX4 has had reliability issues with it. There is one exception, with one driver, who is extremely good. The rest of them break their stuff. The steering rack is weak and tends to snap on the serrated portion where the horn mounts onto. A friend of mine broke two of those in a single event. The 2mm pitch belts are an issue (other belt-drive vintage 4wd buggies use 3mm pitch belts, which are much more durable), and servicing them is a major operation. The rear of the chassis can crack around the screw holes. The front arms are like original B44 arms, in that they're not that beefy (CAT2k or YZ10 arms are much stronger). The inner camber link ball stud mounting holes do not have a lot of surrounding material, especially on the front tower, so they can snap off. In fairness, this is an amazing car. It is extremely quick, aided in no small part by how light it is (which is also what makes it fragile). Definitely easier to find, and find parts for, than the aforementioned, but in my view it is not a "true" vintage 4wd buggy. You can make a CAT2k or YZ10 just as quick by being a good driver.
Tamiya Avante, Egress: I have run an Avante 2011, and I'll just say it looks better than it drives. It has been a few years and I've learned a lot since then, so I'd like to take it back out and do some more tuning with it. But even still, there are better (and cheaper) options. An Egress or Avante 2001 (basically a cheaper Egress) would be better, but I haven't tried either. I have the parts to throw one together as a runner, and maybe I'll do that one day if I have the time.
https://www.youtube.com/watch?v=HUpVRuqnd_I
Tamiya Top Force: Based on the TA01/TA02 platform, it actually drives quite nicely and is reasonably adjustable (I've only driven mine in the driveway a few years back, but it is really quite good). The only thing that really lets it down is the poor quality plastics used for the intricately-molded gearboxes, and the steering rack has some slop. If you can get your hands on some J-parts (or a suitable substitute), you can throw together a Top Force-like chassis without too much trouble.