MP is very variable, thus it requires many runs through to get a good snapshot, an average of 10 games on a 64 player map would likely yield a very accurate representation.
This is why few sites do it at all, doing 1-2 run through is highly misleading.
Even 10 runs can be wrong though.
Situation :
8 rounds on each are purely average.
2 rounds on card A are heavier than normal due to server lag / glitching / super coincidences (squad all using big vehicles, blowing up lots of enemy vehicles in view of player, etc)
2 rounds on card B are lighter than normal due to X, Y, and Z (eg; a squad of players taking a break to go take a dump, eat, whatever, being idle)
That could seriously cause card A to look slower than it is on average, and card B to appear faster.
This is why the only thing to do is bots + scripting + locked server. For the test PC, it wouldn't be able to tell the difference between a real match and the test match.
Given how Origin and EA/Dice work, that's probably unfeasible. But until it is, take any MP testing with an absolutely epic grain of salt.
Cliffs : want to know which is the fastest video card list for BF4? Look at SP. MP will be heavier, but it won't cause cards to flip around in position nonsensically. 290X is still fastest, etc, along with 770 > 760 (derp).