Who here has used them on game & what was the performance like?

I have loaded the 150 Nosler BT in my '06 and used it on deer. Performance was good. I might be drawing a buffalo permit and in Wyoming the minimum weight bullet allowed is 150 gr. I don't think a Nosler 150 BT on Buffalo is a good idea. So I was thinking of working up some loads with either the GMX or TSX.

I can't say on the gmx, but can assure you the Barnes are great. Few deer like on my experience with the but several deer elk, and hog by my uncle and were all great performing bullets .

I have killed A LOT of deer, groundhogs, and some larger game with both.
Triple Shocks are great. Lots of damage and penetration.
GMXs expand a little less and penetrate a little more than Xs. I've killed deer out past 400 yds, with GMXs. Most dropped on spot. I use the GMX when I don't want to destroy a lot of meat. Worked great on springbok in Africa.
Did a deer last year at 380+ with .338 TSX(.338 Mag. JDJ)-thrown to the ground, lots of damage.
One caveat. Less than .264 TSX don't expand or penetrate well.

Can't say much about the GMX other than I couldn't get them to shoot in my 270, but the Barnes TTSX bullets have beeen a lights out performer for me on everything from pigs to bear. Though the Barnes do copper foul like crazy.