I disagree, partly, because with a 7.62 you don't need a burst to knock someone down. The only reason we use burt fire in CQB is because one round usually won't do it. There was a story in Northen Ireland where a provo shot a brithsh soldier using an AR18, .223, the British soldier went down, then promptly got up and shot the provo back with an L1A1. Quantity doesn't mean a thing if the targets you hit don't go down.
I agree that 5.56, 6.8SPC etc.. are classed as a light weapon rounds, 7.62 as medium and .50 cal as heavy. 6.5 offers a merger of light and medium and as a result you don't have to choose between one or the other, which seams to be an ideal scenario.
If I had to go into battle tomorrow with a semi-auto only weapon, I'd take 7.62, but that's just my opinion. I've used both in combat and still prefer 7.62.
Another factor is that full auto fire makes for lazy marksmanship, and beyond 50-100 yuards is basically just a waste of ammo anyway. Discussions with fellow instructors and my own experience shows that most people prefered the 7.62, even in single shot for CQB, the real benefit of the L85 was short length and cut down L1A1s were just as popular when used as an experiment.
Here's another benefit, awhile back I had a tango hide behind a wall next to a window, so I shot him through the wall. Caliber 7.62. On breaching the lower floor we heard tangos above us, so our gunner took the gimpy (M240) and sprayed them throught the ceiling, caliber 7.62. The way I used to discuss this when instrucing courses was the following, decide which bullet you would rather be hit by, and then carry the other one. After the engagement when heasrding enemy wounded, most were hit with 5.56, fery few of the 7.62 strikes resulted in walking wounded.
The 77 grain .223/5.56 is nice but a 147 grain 7.62 hurts more. As an option 6.8 is nice to 400, but 6.5 is nice to 1200 and a little heavier also.