Check out my option parts that I have been using during the 2015/2016 winter season at EOS races. The following parts will improve the overall performance of your XB4 on carpet tracks.

#363352 & #363351 Alu Uprights
Gives more rotation from the rear end of the car, which allows my XB4 to turn faster in corners.

#366220 Servo Mount
Gives additional increased steering and improved flex.

#362573 Alu Steering Plate
With improved & increased steering, you should improve steering predictability. This steering plate increases steering predictability, and it gives you additional set-up options.

#362478 Anti-Roll Bar 1,8mm
More steering also means more chances to flip your car. I use these anti-roll bars at both front & rear ends of my car to avoid traction rolling; they are perfect for the high-grip conditions of EOS carpet.

#369704 Lightweight Body
This is another very good option to avoid traction rolling, and the lower weight of the body improves your landings.

#362112-G, #363121-G, #313111-G Graphite Arms
If you have more steering, you may want more cornering speed. The graphite arms give more cornering speed in high-grip conditions.

#335030 Diff Bevel & Satellite Gears
These 'last but not least' option parts offer much better durability and a better traction feeling.