The 4 gear is a lot better as an overall package, but you do need to change a few things on it to get it working really well from the 3 gear.
Basically you need to remove anything you had done to get rear traction with the 3 gear, so if you have any extra weight in the rear then remove that, lower the gearbox and make the wheelbase longer.
My old setup was 30 grams of weight either 0.6 or 0.9 under the gearbox and full short on hubs and arms.
I now run no weight, gearbox with no spacers and long wheelbase. The only time I change the wheelbase is if it is really slippy such as damp astro but for indoors or normal tracks I run long.
I was also strongly suggest the Espeed camber extenders if you don't already have them as this will help with the steering.
For really high grip tracks I am currently playing with a rear roll bar to help get the car to steer a little more as well. Just need a high grip track to try it on now as it just keeps raining down here
