No downside to 7” twist, unless you want to push thin-jacketed lightweights to 4000fps, in which case some of them might dissolve in flight.
OTOH, a 7” will let you shoot anything out there that I’m aware of, and you never know when the bug for something different might bite.
If you were buying an older gun with a 1-9, I’d say go for it. Since you’re paying for a new barrel, why limit yourself?
