Here's another vote for the 6.5 x 55. I dearly love my 1903 MS carbine, and personally would prefer it, but if I were to commission a new custom rifle on a modern action I would choose the peppier chambering without hesitation.

The Swedish 6.5 is extremely under-rated for medium-game IMHO. The .243 would have been still-born if Americans weren't so metrico-phobic!