I use poly mains and syn gut crosses. I like the feel of the reverse, but like you, found that it doesn't last long. I play a 16x20, and the strings still move a lot even with the denser pattern. I generate a lot of spin, so depending on your stroke, you may find different results. The thing with these types of hybrids is that the mains move, so for durability's sake, you need something tough or slippery. I haven't tried gut/poly, but that seems to be all the rage now.
IMO, I'd stick to poly mains and multi crosses since you've had success with it. Someone else might have some advice on a durable setup like this, though. Good luck!
PK 7G w/BHBR 17g X Weiss Cannon Silverstring 17g @ 30lbs