i also play with kb stabilised and i'm very competitive driving the fwd cars at tracks i know. i'm pretty good with 4wd's too but it's hard to catch a slide when the tail drifts out.
the biggest problem with kb is consistency because u can't make small corrections and thus if u screw up a line into a corner u will suffer a lot more than if u had a wheel and pedals. making a little mistake with kb results in a big penalty.
the 2nd biggest problem with kb is racing against other people. swerving to avoid hitting other cars or to simply make an overtaking manouver is hard because you're not in "complete" control of the car.
u will never become as consistent as u could be with a wheel but practice makes perfect though