Thanks. Yes, wrong forum, early start and not thinking!
I currently use Polyfibre Hightec Premium @ 55 lbs in my Extreme's. A nice soft poly, but I have no experience with the Pro Staff so not sure what I can get away with.
Good stuff, and it sounds like you have your preferences figured out so hats off. The PS90 is a very lively frame even if it's control oriented due to the small head and flexibility, so you can't go wrong with a poly.
I'll even say - try the same string setup you have now. Saying this for two reasons:
1. That way your comparison is completely racquet to racquet
2. At least to me, soft polys/ stiff polys at low tension gel awesomely with the PS90
After you've tried your own setup, report how it played and work from there
And most importantly enjoy it, this racquet is a treat!