It's amazing to me that you could break kevlar after 3-5 hours. You either hit very hard or string it very tightly. I'm also surpirsed to hear you say kevlar doesn't last longer than polys.
The first time I play with Kevlar (moving from some poly or synth gut) I noticed a huge drop in power. It was frustrating. But after a few weeks I adjusted; and saw that the string didn't move at all and was wearing very little. OMG, I love it cuz that mean i'll not have to spend every few weeks.
My apdc has kevlar mains and poly crosses at 55lbs. I could use more power by lowering next time. I also strung my pdgt with same set-up but at 50lbs.
Today I just bought a few more sets of kevlar and co-polys.
Be sure to string low and hit with more power.