One of the reasons I picked up my two 6.5's is that the Baffin Co-op's had almost 1000 rounds of ammo that must have been mixed up with 6.5x55 orders over the years. Unsold for decades, I bought most of it at 5-10.00 a box. The factory ammo is wonderfully effective on caribou!
I then looked for and found two rifles the 660 and the Ruger. In those multiple lots of brass the average is very close to 70 grains capacity, of water. I have found the difference between the 6.5 brass and my 284 brass to be greater than that outlined above in favor of the 6.5 Rem Mag.
I had a 260 Rem but soon sold it when the 6.5 Rem's very easily gave me 150ft/sec more in the same barrel length with equal or better accuracy. I found it much easier to get accurate loads in the velocity range I wanted as hot rodding the 260 often led to poor accuracy. The muzzle blast and recoil that people speculate about hasn't been a factor with my 6.5's but the original 18.5" barrel might be too much of a good thing.
As Jack O'Conner found many years ago a 130 grain bullet at 3100 fps is a beautiful thing. I have tried all manner of small bore magnums but keep selling them off and keeping the 6.5's as they seem very well balanced to me. I'd probably be as happy with a .270 but the 6.5 is a bit unique and ballistically identical. Pretty good company to keep.
Might even keep the 358 Norma at home next year and take the 660. A 140 Nosler at 2900ft/sec ought to do a nice job.