It is a very fine cartridge for North American hunting with far better killing power or anything in that class.  In fact, every species of big game on earth has been taken with this cartridge.  A great many elephants were taken by ivory hunters using the little 6.5 and solid bullets.  It did not make enough noise to bother the herd and gave deep penetration for well-placed brain shots.  In the hands of an experienced hunter, it will do for any North American big game.  However, by today's standards (written in 1993--Mark), it is primarily considered a deer, sheep, antelope, or black bear cartridge.  In power, it is often compared to the .257 Roberts, and there is some validity for this.  On the other hand, the 6.5 M-S is loaded with bullets of around 160 grains in weight compared to the top weight of 120-grains of the .257.  It is the long, heavy bullet that makes it a good killer on the tough varieties of game.

All this speaks well of the 6.5x54 M-S, though it really doesn't address your original question, that of how well it works for longer ranges.

I did find this thread on "Africa Hunting" that is moderately useful:

6.5x54 M-S at Distance