BE XM8? *Snort*
Tokyo Marui G36C, then modkit it into an SL9-SD. Slap on a 3000-round double-drum magazine, a 9-12x40mm zoom scope (if you've got the cash, get a green-light), an under-barrel bipod, and then crank the power to 400+ FPS (400 is usually the tournament limit [at least, back when I was still interested in airsofting]), and then come talk to me.
(Plus, all this'll only run you about $500USD... if you do all the modding yourself. If not, be prepared to shill out something like a grand...)It's the ultimate sniper's/field combat weapon. Fully-automatic with a 3k double drum mag... and 400FPS. You can almost kill someone with it. (You could if you shot them in the eye... but anyone airsofting should be wearing protective gear, or they shouldn't be airsofting).
I wouldn't recommend the setup for CQB, though. It's kinda big ('cuz, y'know... it's an SL9-SD [or SL8; you can shorten it by a bit by not taking along the {mostly decorative} silencer]).
-- Griffinhart
PS. And in case you're wondering, no, I'm not an airsofter. Not any more. Not since I found out it was illegal for minors to airsoft... v_v