Is there a reason you believe the shimano would be an upgrade? The PG-950 is a pretty good cassette and SRAM even makes some better cassettres if you must upgrade. Or would you just rather have a cassette that matches your shifters? I been there when I got my Klein. Everythong is Dura Ace. Hubsm Cranks, bottom Bracket, brakes, shifters, seat tube Head set and rear Cassette. The problem was the rear Cassette was a 12x23 and the chainring in a 52x39. I simply can't climb worth beans with 39x23 so I had to think about another cassette. Ended getting a SRAM because a new Dura Ace was way too expensive. Not Campy expensive but a lot more than SRAM.

Normally people go through at least three chaines before they go thtough a rear cassette. Unless you go way past the stretch limits of the chain or ride hard as a MTBer.