I"ve had thin skinned 64 bergers come apart in my 6.5 twist.
But in the 6.5 I've also shot quite a few 52s...
I just won't shoot junk like FMJ so can't help you there. At the worst, cheap bulk softpoints every time over the FMJ.
7 twist is one of my favorites, it will shoot 52/53 thick jackets. It will do great wtih 68/69. Shoots all of the Barnes versions. Works great with all the 70ish grain mag length loads. And does super fine with 80 single loads.
Can't beat taht IMHO. And I see no use in light bullets unless was limited to short range shots.