What's the hang-up with wanting a repeater so bad? I have a 260...
My 260 by MCR
It is my long-range rig for varmints (as far as I can see) and deer out to 900 yards. It is a single shot. I have no problem getting a second round in the chamber quickly.
My next build is a 300RUM and it will be a single shot. It will also be a dedicated long-range rig and a single shot.
I do not/will not feel handicapped by either of these rifles being single-shot.
Now if you're building a carry-rifle, then you will probably want a repeater. Here's my 280rem carry-rifle....
My 280 - Updated!
In terms of caliber, my approach is a bit different than one stated earlier. Rather than choosing the cartridge, I choose the bullet I want to shoot, then find the cartridge that will drive it at the velocity I 'need'.
Since it sounds as though you want a 6.5mm (they are badass!) there's little that a 6.5Swede won't do. You can shoot 142SMK, 140 and 130VLD really fast (3000fps +)