I sold my kicker kx800.4 and bought an infinity 7540. Both are sold as 100x4 amps. The infinity has 1/2 the fuse rating 60A vs 120A. The infinity is 1/2 the size.
The infinity blew away the kicker. With the kicker the sub would start clipping before it ever got loud. With the infinity it gets extremely loud, no clipping. Car audio is full of surprises who would have thought an amp half the size and half the fuse rating would be better?