The slowdown seems to be general. My system takes ages to start up, browsing & opening windows takes forever. I know it's not 100% accurate, but my CPU meter gadget shows the CPU running at 100% all the time (Without the card installed,it's about 35-55%). I've disabled all but the very basic start-up programs & still no change.
I've not run Benchmarks. I've heard of it, but don't know much about it to be honest. I'm far from a newbie at this, but wouldn't say i'm advanced either!