321 hours would be considered "high" by many, but it really depends on how well it was maintained. I sold a 350 hour GTI 130 that was running like new. My GTI 155 has 260 hours and is also running like new.
I've also seen ski's with under 100 hours that are trashed.
The "pro" models have upgraded components, such as electrical harness, driveshaft, wear ring, rental seat, handlegrips, so that's a plus.