As far as durability goes, Kevlar is the best you can get, hands down. Combining that with NG gives you the best of both worlds (except in wet conditions). I would try a multi or synthetic gut in the crosses for those wet conditions. Most Poly string goes dead in a very short time and loses it's ability to snap back, usually causing arm problems if you have poor stroke production.
Add to that, a recent test conducted by the ITA states that Poly string only adds about 3% increase in spin compared to other strings, and that is totally dependent on your swing (if you don't have a topspin swing, you will not get topspin no matter what the string).
So you can try other string just to see how it feels and if it works for you, but you have a pretty sweet setup now. You know the old saying "If it ain't broke, don't fix it". BoL
Cheers, TennezSport :cool: