Guntech,
A different means to the same end. What is telling in these discussions is the utter lack of people advocating a smaller caliber. Why no 20 cal. Super Streak at 3,500 FPS? Because most people realize that there are benefits to be had with larger calibers, mostly .264, .277, and .284.
Do I think we could adopt one caliber for everything? No. I think a lot of things will remain 7.62x51 for a long, long, time. We COULD adopt a new cartridge that replaces the 5.56 and 7.62 for infantry rifles and even infantry portable belt feds, but I think different loadings would be beneficial. Tactical long range stuff is special stuff anyway so no reason it couldn't be a 6.5 or 7mm loaded with a different bullet to a slightly higher velocity. No reason we couldn't have a dedicated load for the belt feds too, something that you could use in an infantry rifle but would be a little hotter than regular stuff.
The primary concern is performance of the infantry rifle and especially the M4 carbine. The fix is in going to a larger caliber with more power, while still being somewhat controllable in three round burst. Using bullets with a high BC will allow fexibility of the cartridge, but for distance it will likely be a special round anyway. I guess I'm trying to say that getting maximum BC in the "standard" rifle isn't going to be a priority.