Since patch 0.8, I've had had the same problem with all my multi's game.
So, I start a single player game, 4v4, with AI's, and the game doesn't lag at all, everything is marvelous.
Then, I do a 3v3 online, and the game is laggy to the point of being unplayable, with my CPU apparently at 71 while it's barely at 30, and if I quit the game then redo an AI 4v4, the game is once again laggy as hell.
I'm certain that it is not a client-side problem, since I was able to play 4v4's online before the 0.8 patch without the slightest problem.
So yeah,
Cordially,
SX23.