It really comes down to what bullets you want to shoot at what velocity. If you're planning to shoot 109s or lighter, I'd go 6bra in a 28in tube. This will allow you to rub 2800ish and not be dangerously close to pressure. Want to run 110-115gr bullets at the same lower pressure 2800-2850 range, run a 28in 6gt.
I do feel that raw accuracy edge goes to the br variants. When they're really tuned we'll, accuracy at distance in minimal winds is in the 2s and 3s, 10 shot groups. The gt is just slightly bigger. I however did have one 6gt kreiger tight bore that shot 108bt for in the 2s and 3s very consistently at 400-500y on paper. However don't use a tight bore 6mm, for any these cartridges that are not strictly bench use, carbon rings and fouling can become a problem really quick without religious aggressive cleaning. 237 bore all the way.......
I do feel that raw accuracy edge goes to the br variants. When they're really tuned we'll, accuracy at distance in minimal winds is in the 2s and 3s, 10 shot groups. The gt is just slightly bigger. I however did have one 6gt kreiger tight bore that shot 108bt for in the 2s and 3s very consistently at 400-500y on paper. However don't use a tight bore 6mm, for any these cartridges that are not strictly bench use, carbon rings and fouling can become a problem really quick without religious aggressive cleaning. 237 bore all the way.......
