A 185 E4 doesn't slow you enough!? Is it set up/bedded in correctly? Whatever the problems on the front, I can't imagine ANY disc brake not working on the rear, even canti's can lock up one o' them.
get a 185mm rear, upgrade the front to a 205mm, i doubt you really having probs stopping, if you are just pull harder on the brakes, i now guys that fly DH and can stop using Vees, and they weigh same as and more than you