I made a small design comparison between the 501X and 511 a few years ago.
http://www.tamiyaclub.com/showroom_m...87535&id=13377
In my opinion there is a
huge difference when it comes to maintenance.
If you look at photos you will see that the 501X was like an onion with several layers of parts on top of each other.
If you wanted to remove a diff you had to remove camber mount in order to remove the damper tower, in order to remove the top deck.
After that you could remove the diff. Well, you also had to remove the diff cover. But that diff cover design mistake was same on the 511...
So ~10 screws later, with parts all over the pit table, you could finally access the diff.
The front (rear) suspension mount had to be removed in order to replace the rear drive belt. When you did this you had at least one suspension arm hanging in the turnbuckle. You were lucky if you didīnt loose any shims or suspension balls.
At the front you also had to remove the tube between the center bulkheads.
So you could add 2-4 more screws to the list above if you wanted to change the drive belt.
There are more to tell, but I think you get the picture.
Performance, probably no difference for average driver.
My thoughts...