I dont have any experience with the 6.5 rem mag, but i do with a 6.5X55 in a 700 classic. The way i look at it is, if you are looking for a long range set-up then go with a long action. The 6.5-06 AI is a really good wild cat, or the 264 win mag is even more potent.
I personally, do not like belted mags, theres no need for the belt, so why have it? If you want a short mag take a good hard look at the 7mm saum, yes its a dead round, but you can buy Rifles chambered in it for a song and a dance. There are tons of great bullets, and its ballistics mimic the 280 AI. I bought one in a stainless, synthetic, model 7 and its a great little, accurate, rifle.
With that said, if you want a different cartridge that no one else will have at the range, go with the 6.5 rem mag, but a 6.5 saum would really be different. The saum case has a long neck, is more tapered than a wsm, and its capacity is very good, Norma also now makes 300 saum brass.
