Not sure if this will be of any use to most of you however if your CPU cores are being lazy and not doing anything other than Core 1, try using these launch parameters for your game.

Under Properties -> Launch Options.

-nosplash -noPause -world=empty -noFilePatching -maxMem=8192 -cpuCount=8

Edit it to the number of Cores you have an the amount of ram you have.
I'm using i7 3770K with Hyperthreading so mine is 8 for example. However i5 3570K would be 4 etc.

Ram sizes:
1GB = 1024
2GB = 2048
4GB = 4096
8GB = 8192
XGB = X*1024

Hope this helps a few of you improve your performance a bit :)

• iKingyx