I'm a 4.5-5.0 player. I hit quite hard and with plenty of spin, and I would no longer consider playing with strings that are less spin-friendly than poly.
I also would be breaking strings in less than an hour if I used syn gut.
My contention is that even 10 hours of play is a ridiculously short playing life, and that the tennis string industry has a good scam going with the this poly craze.
I'm a former Problend user (used it for more than 15 years, strung at 77 lbs in a Wilson Profile OS). Problend would last me about 30 hours in that racquet before it broke (where syn gut only lasted 30 minutes at that tension).
I currently use Kevlar mains (crossed with poly) because it let's me keep playing with decent stringbed performance for 20, 40, even 50 hours. However, I'll note that I'm finding myself stringing this combo somewhat tighter than I did at first, because the poly crosses do lose quite a bit of tension over time, and once it does, control can suffer. I like to string it so that it will feel perfect after the poly crosses have stretched out. It stays playable because the combo never loses it's string-in-string lubricity.
Kevlar dies very quickly... no arm or wrist issues?