While I don't have direct experience with the amp, I did read about the amp on the Mesa site. It supposedly has it's drive channel w/ contour designed to be like the Dual Caliber series. This is what I will mainly comment on. In my old basement band, the other guitar player had a DC-5. With that amp, on the drive channel with the help of a TS9, he could get pretty damn good Trey tone for Phish tunes. Using a Tele w/ a humbucker in it Incredible sustain and thick texture of sound. So if that is any indicator and that is part of the sound you are looking for, this amp sounds promising. The downside of the DC-5, imo, is that the clean tone is anything but. The clean channel was not all that clean. This compared directly to my Peavey Classic 30 clean channel. The F50 claims to have the clean channel design taken from a studio amp w/ studio clean and my guess is that for alot of GD tunes, that will be the telling channel.
Good luck with it. Hope the dude lets you check it out and it has the various tones you are looking for.
The river keeps a talkin'