Depending on what you want to use it for you can go with a 260 (6.5 308) and all of the WSMs and SAUMs I have a 338 RCM on one and it is awesome. also a 7/08 on one .
There are lots of rounds that will work because the magazine is the same length as the short action 700. A 40x or XP Jewell trigger will also work.
You can build virtually anything with your donor action. The least expensive option will be a chambering that does not require you to change the bolt-face. So consider the cartridges in the 308 family: 243win, 260Rem, 7-08, 308win, 338Fed. Among these, I think the 260 is most versatile.
From the research and the advice that I have gotten from this site and others. You would probably get more from the 6.5 creedmoor cartridge. I have recent started working on getting th supplies for a similar build in a Savage action.