Last night I was getting slowdowns in the same system, steadily dropped form 60fps to 12 or 15.
Dropping out of SC & back into SC fixed it for a while.
I suspect its the sheer number of players… I would have seen a good 15+ all skipping around looking for these invisible warzones.
FTR I’m on an i3 3.1 as well but have overclocked it to 3.8 and bumped the ram up too.
7870 Graphics too. When I do resource monitoring, its my CPU pegged @ 50% so assuming no hyperthreading being used thats 100% load.
Whats your internet speed like? www.speedtest.net