Whatever you might have.

Not mine and no connection to it -

6.5 Rem

I'd punch it out to 264 Win.

It's pretty much a 6.5-06 in a short action.
I have an old Ruger flat bolt in 6.5 mag. Used it some, then stacked it in the corner and went on to my next "perfect" rifle.

6.5 Rem Mag is a great round.
Availability of brass is it's biggest obstacle.
.338 Federal, same thing, but the list of cartridges that have fallen by the wayside due to component availability is long.