I would second the 6.5/284 it is about the single most efficient case design there is, however since you stated you did not care for the rebated rim my choice would be the 6.5×55 AI. It IMHO is a very close second. Anything beyond these two in a 6.5 is going to be overbore and anything less would not be any better than the creedmoor you already own. I have owned and hunted with 6.5×55, 6.5×284, 6.5. Creedmoor, and 6.5 Ackley. They were all excellent shooters. I presently own a creedmoor and I am considering another 6.5×284 build on a Sako action. I really like the 6.5 caliber but you do not gain much with the over bore cartridges and barrel life goes in the tank pretty quick. I shot my last 6.5×284 built on a Nesika action for bench competitions about 15 years ago. I put close to a 1000 rounds through it before I traded it and never shot it out. I am presently playing around with a 338 RUM which also has a rebated rim. It is on a Remington 700 action. Neither it, nor my 6.5×284 have ever given me any issues with a combined 1200+ rounds through them. The 6.5×284`in my opinion really is just about the best variant of the 6.5 there is and one of the best cartridge designs out there along with its big brother the 284 winchester. Both way ahead of there time have won more benchest competitions than most other cartridges combined. Whichever you decided to build I am sure you will enjoy it. Both the 6.5×284 and 6.5×55 AI are excellent cartridges and are basically ballistic twins.
