I'm not into 3 gun competitions, but I have set up one of my rifles to be lightweight and fast. Fast follow up shots that is. I've got the Battle Comp 1.0 on a Daniel Defense mid length upper. There is a world of difference between my issue M4 and my personal gun. The Battle Comp makes a big difference. It's such a flat shooting rifle now. A quick Google search will bring up lots of reviews and videos.
Check it out.