I daily carry a Kahr P9 Covert and KelTec P32. I've owned numerous other poly guns and have never knocked them. I'm generally a high-tech kind of guy and embrace new things.
Having said all that, the smaller poly guns such as the PM9 will wear out more quickly than the steel versions will. The hotter the ammo, the quicker they will wear out. If you have 50 rounds of the Ranger, I'd go shoot it up. If you're the kind of guy that feels completely comfortable and confident in a carry ammo after putting 50 flawless rounds through it, then the +P+ Ranger stuff may be exactly for you. If you're the kind of guy that wants to see 500 rounds of carry ammo through the gun before you're confident with it... well... that's a lot of wear and tear on the gun.
I carry 124 +P Gold Dots in my Kahr and I've recently out 60 rounds of 115 CorBon +Ps through it as I heard it that was the round the Kahr's were designed around. I feel confident in either of them. I'm sure the Rangers are just as effective as either if not possibly slightly more so. Again, I'm not going to put 500 rounds of the Ranger through my Kahr to find out though...
Either way, good luck with the shooting. Be sure to let us know the reliability of the ammo in the Kahr and how you feel the recoil compares to standard pressure stuff...