At long last we can join the masses.
I have been forced to compromise. Using Frets On Fire I turned my keyboard upside down and pretended it was the same but at last my time has come. GHIII completely obliterates FoF in the department of scrolling tablature slash mp3 player. The controller can be used to play FoF, which I did try but ultimately felt lacking.
The songs are quite challenging. Playing FoF I was able to consistently score 5 stars on expert. GHIII's Hard is more the Expert level of old. Talking with friends who owned the previous console version have confirmed that for me so it's not just a FoF thing.
As for the performance issues, I couldn't say. I run AMD X2 5600+, 2 gigs DDR2 cas3, Raid 0 WD raptors, and an 8800 GTX. Load times are too quick to read the tool tips, and I have yet to notice a single hiccup. Although if your just looking to play GHIII it would be much cheaper to just buy a Wii :/
I'm just happy at long last to have my own little plastic toy guitar. Although now when I play with friends I can no longer claim "If this were a keyboard I would own".