Maybe a late reply on this issue, but it got me started solving my own issue: engine stall ~600ms and 20+ network lag spikes. Just gonna post it for people who have some sort of problem that looks like mine in a hope they can fix their sc2 problems as well similair to this. This solution solved my engine stall + network lag spikes.

After installing my new Samsung 840 Evo, I just simply copied the SC2 files back to the original folder @ the main drive together with the battle.net folder for the desktop app. When I did it the first time, swapping my old hdd for the previous ssd, everything was just a simple copy and paste away from playing: start batllenet updater and wait a few sec to find/create the folders it needs. I've been playing for several hours without any problems. Even after optimizing the game, adding some lines in the variables.txt and doing some more (after this guy his guide: Handy link ).

But after some fun I wanted my savegames back and the status in desert strike (arcade game) which are not saved remotely, like your achievements, ladder ranking or statistics, but simply on your pc. So without any doubt, I just copied the backup of these folders and just replaced all files.

C:\users\%username%\Documents\Starcraft II
C:\users\%username%\AppData\Local\Battle.net
C:\users\%username%\Documents\Roaming\Battle.net

I did this before I went to sleep. Though it was just a couple of seconds, I went to bed after being up to date at facebook, what did took a lot of time today on google to solve this issue. But when I realised it, I deleted these 3 folders and relogged @ updater app and started without any problems a new game on desert. Though, my savegames where gone but the game has never been so smooth @ higher (default extreme) settings with more FPS!

So if you are having performance issues like you can't play on higher quality anymore like you used to play before, or having engine stutter/lag spikes like me: try to delete one of these folders 1 at a time to see if it works. Don't worry about any problems, the game itself will recreate them again once the game is started.

**Warning: do this on your own risk!!**

If you decide to completely delete the starcraft II folder inside your documents folder, all your savegames and game settings are lost.
So make sure that you have a backup of these folders in case your sc2 problem is not solved so you can recover your settings and savegames of the game.