Both of my 6500CS M-Es are spooled with 20# Berkely Big Game (green). Some people use braids to increase strength and capacity but unless you are fishing the Ditch or seriously long-tossing baits, do you need the capacity??? Maybe Saltheart can chime in as he uses several braids on his 6500 class reels...
Good luck, that is a very sweet reel - wait until it's broken in <img src="/Images/biggrin.gif"><!--e7-->