The 6.5 CM lives up to the hype. It is about the perfect balance of bullet weight, velocity, recoil and accuracy to hunt anything in North America as well as being suitable for target shooting out to a mile. This photo explains why.
And for the record, the 260 and 6.5X55 are capable of doing exactly the same thing as 6.5 CM. But the 6.5 CM does it with factory rifles and loads. In order to make the others work requires hand loads that are out of spec., and custom rifles. The 6.5X55 was designed around 160 gr RN military ammo @ 51,000 PSI. The 260 was designed around 120 gr deer hunting bullets. In order to make either work with modern high BC bullets requires tweaking of both loads and rifles.
The bullet on the left is a 143gr 6.5. Next in line is a 150gr 308, 178gr 308, and 200gr 308.
Compared to the 150 gr 308 I use 5 gr more powder with a 7 gr heavier bullet that leaves the muzzle 150 fps faster resulting in 25% more recoil. The longer 6.5 bullet out penetrates any game animal at any range. Trajectory is virtually the same for 400 yards, but beyond that the 6.5 wins. At only 200 yards the 6.5 passes the 308 in energy. At 800 yards the 6.5 has about the same energy numbers as the 308 has at 500. Beyond that it isn't close
If we move up to the 178/180 gr 308 loads we see a more even matchup. At that bullet weight 308 will now match 6.5 in penetration. The 308 with the heavier bullet has an energy advantage at the muzzle, but the 6.5 catches up within 300 yards and both have enough energy and penetration for elk. But the 308/180/@ 2650 now has significantly more recoil than the 6.5/140 @ 2700. For zero gain in performance. And beyond 500, it isn't close.
It is only when we move up to the 200 gr bullets that 308 has any advantage over the 6.5. And you really need to be firing them from a 30-06 or 300 WM. At 308 speeds energy and penetration are better. But now trajectory and recoil become serious concerns.
Considering that most 308 shooters use 150-165 gr bullets a 6.5 with 140's is an improvement.