Powerlevel in HG but not with your main that's really important, you have high risk to get banned. You'll need 4 computer for this. When you're ingame, go to the enemy spawn with the computer 1 and 2, spawn mercs with computer 3 and 4. When you don't have anymore cash you spawn bot on computer 1 and 2. With this you can get 20,000 exp per game with 200% exp boost but you'll need something like 500 kills per game.