With 1:9 barrel the heaviest bullet that I will use is a 62gr with lead makeup and 55gr no lead makeup.
My XM177E2 will not stabilize a M855 62gr. It has a 1:12 bbl. Found this out the hard way in 1970.
I am a huge fan of fast(er) twist bbls. Nowadays I have no .224" bore guns that do not have a 1:7 twist,the exception is the above mentioned retro build.
I have no use for a 308Win with anything but a 1:10 twist bbl. A 1:9 would be better. I do not believe that you can overspin a bullet. 350,000RPM is doable. A half million and higher with the right bullet. Example: I have a Bison Armory 18" 6.8SPCII. It came with a 1:11.25 twist bbl. They also offer a 1:7 twist bbl so you can shoot long/heavy bullets subsonic. You can also shoot lighter supers from this bbl with great accuracy. The bullets will not come apart,explode,melt,go into outter space,etc,etc. 11.25 vs 7 . . . that is a big difference.
The above are my beliefs. YMMV --- SAWMAN