6XC - stupid easy to work with and cheap to shoot, 3000fps with 115's. Nearly a mile supersonic. Super mellow recoil.
.243AI, 6mm Rem AI, 6-.284 - .473 bolt face awesomeness. Run 115's to a mile+ supersonic. with very low recoil. .24 cal is a little short on barrel life but unless he's a competitor it's not something you'll worry about for a long time.
6.5CM - don't let the pedestrian velocity fool you. 140's go FAR and it's very easy to learn on with mild recoil and blast.
6.5x74L - Better case design than the 6.5CM with virtually identical performance.
6.5x55 AI - 3100fps with 140's. Like a 6.5PRC but lower powder appetite.
.264WM - I just don't like belts but it is a way to get 6.5 bullets going stupid fast. Not enough of a gain over 6.5x55AI for my money.
7mm-08AI - All the performance you need to go to 1500, easy to shoot well, mild on the shoulder, small powder appetite, hits harder at long range than anything else I can think of with the same case capacity.
.280AI - Nearly 7mm rem mag performance. Nearly. All the way at 7mm RM levels for recoil and blast. Really an unsung hero. Berger 180's fly faaaar. It's nearly a magnum.
7RSAUM - If you're going to magnum then ditch the belt and throat the barrel long and you've got a long range toy with a ton of stomp at the long end but not severe recoil (about .30-06 level unbraked).