Personally, i see no downside to tighter than required twist. If you shoot well constructed bullets with minimal run out, tight twist offer nothing but benifits. The largest being consistent B.C. in all conditions.
After my last twist test, and reading bryans book, for now on all my rifles will wear a twist at least 1" faster than recommend.
I've seen a number of guys go down the more is better with twist rate and many ended up having to shoot bullets they did not want because after a few hundred rounds the highest BC jacketed bullets would no longer hold together. There is no benefit to twisting more than required for stability and accuracy IMO.
I went thru this decision process recently. After reading, researching, and asking some members that shoot a lot of .338s, I concluded the only reason to go with a faster than 10 twist in .338 was if I wanted to focus on shooting monolithic bullets. The monolithic bullets cost substantially more than the lead core jacketed bullets. And the ideal twist rates are different enough between these two different style bullets that I couldn't identify a compromise twist rate that I felt would work well with the best of both style of bullets. It was either buy a twist rate for the monolithics, or buy the twist rate for the jacketed lead core bullets.
It became too complicated, there was the extra cost for a non-standard twist rate from Bartlein, so I finally ordered a standard 10-twist which I decided was just fine for the 300gr lead core jacketed bullets such as Berger and Sierra.
Just took possession of my first 338 Lapua built by Phoenix Custom Rifles. I'm running a 27" Bartlein with a 1/9.4" twist. I have loaded Hornadys new 285 gr VLD Match bullets. I fuigured better to have more than less twist so I went with the 1/9.4".