If SRAM is like Campy or Shimano, the higher grade cassettes get expensive really fast. I usually go for the lower grade Campy, either Centaur or Veloce, since I'm not racing. On the usual ride I'd never notice as long as the shifting is smooth, which it is. You would never notice on your bike either so get the less expensive one. And yes, replace the chain too. KMC is fine.