this is exactly what I do on free for all. I use scar or ump with scavenger and I always rape. It's really the way to go if you play FFA. I get the odd message calling me a camper but I could give a poop. I have a lot of fun with it. Add heartbeat to this set up if you have bad audio problems and your almost guarenteed a win.
On S&D I always rush, never sit back. People need to change their game based upon game type. Too many people just run+gun, that's it.