I read that if you kill the agent.exe, the download will be killed and you can play lag free.
This was true for my friend. He blocked the agent download, in a app called netbalancer.
(I tried this but)
This was not the same for me, for some reason, my download, falls under sc2.exe, not the agent.?
Obviously if I block the sc2.exe download, I cant play / download maps or do anything.
When I kill the agent process in the control panel, my sc2 game outright disconnects from bnet. (and I cant reconnect without closing the game)
Why am I using sc2.exe to do handle the downloads, while hes using the agent.exe?
I removed EVERYTHING blizzard, from sc2 to diablo3, I even deleted all files in documents and program folders. (and coped his sc2 folder into mine - made no difference)
Is there a way to stop the download so I can play the new patch?
as you can see in this screenshot, the latest patch is done and my download speed is no where near what you want when facing such a size download. Sorry for my wall, I just wanted to be thorough.

(I even left out some more info I felt wasnt needed or helpful)
http://s1.postimage.org/azvtj664f/sc2update.jpg