The GT's are sweet bikes, they pedal and handle nicely. However, from riding one around a bit I'd say you need to run them a bit undersprung to get full use of the suspension; I'm not really sure why that is but they feel slightly too stiff when they're supposedly set up correctly. However the geometry is pretty good, and like I said they pedal really well. They come with pretty good parts too (to my knowledge you can't get them as frame only this year, which is weird).
Have you considered a Balfa BB7? $4000rrp for the frame, and they pedal and handle really well too. Also the new Iron Horses are supposed to be pretty sick, pretty cheap too. There's the obvious choices like 222s and M1s too, but if you're willing to pay that much I'd check out a Turner too, they feel farkin insane.