My proof prefits in 6.5, 6cm and Dasher all shoot great!
My opinion on the GT vs x, y, z 6BR variant.
Expect you may have to tune mags for GT, expect you might buy mags kits for the BRs but still need to tweak them. I’ve had both cartridges and some mags worked without any tweaking right out of the box… some I could never get to feed.
I just think for every: “I never had a problem feeding.” There’s a “I had to buy 2 mags before I finally got X working.”
As long as your prepared for that, than it’s a wash, a 105 - 110gr bullet at 2750-2900, you’re doing the same thing across all the cartridges. They’re all easy to load for, but factory ammo for the GT is nice. If you’re playing the I absolutely will not reload… 6cm, a lot more options on the table and it’s 100% a competitive cartridge.