the only reason i've yet to decide on 390's is for the lack of cap-strap. though rome makes the most effective convertible toe strap on the market, i just dont feel the comfort as i do from burton capstraps. that being said, anything from customs to p1's from burton are good for freestyle. the triads are the most responsive (according to burton) of those but when i rode them they felt more cush than my cartels. my buddy rides the salomon spx pros with the burton caps and he has so much style and is soo smooth i want to brake his knees. if you're okay without the caps, then i would also highly recommend you check into union bindings.
Go ahead, drink that kool-aid.
FS: Forum Sauce 142 $200 plus shipping
FS: Flux SE30 $75 plus shipping