I run an XB4 and a Caster S10B. I raced them both today at a Regional Championship in the North of England.
The XB4 is a great car, but I have problems with it hopping its back end up in the air over smallish bumps or jumps. The car feels really nicely setup - very similar to the Caster, yet the Caster will fly nice and flat over small jumps and just hammers over bumps superbly.
The Caster is heavier (1.9 kilos ready to race), but I have weights in the back of the Xray to try and help. Anybody else suffer from this? Still qualified 9th out of an 80 car entry, so quite happy.
Jimmy