Well let me tell ya... I have that exact same combo (800JB and the Maxtor Ultra Series 80 gig 8mb drive) and I have them striped in RAID 0 via my onboard Promise controller.
In Sisoft Sandra 2002 benchmarks, it scores 4513, which is higher than any of the included reference scores. I realise this a synthetic benchmark, and not even the best hard drive test, but it's what I have on hand at the moment. If you have the free version of the program (all i have) run your current drive and see if 4500+ seems like an OK score to you.
And this is with the crappy onboard controller with no options for stripe or cluster size. A decent PCI RAID controller card would perform even better.