Which RAW/NEF settings are you using? If you shoot 14-bit RAW, then you're automatically reduced to shooting no faster than 2.5 FPS. You'll definitely want to be shooting 12-bit RAW if you want to get 6 FPS.
Brandon Nikon D80 & D300
"Great art not only brings forth the ordered essence of human experience, but of the world we live in, too - this is what we call beauty. Art and love are man's greatest gifts to himself; and there can be no art without love. Art is always the making of the soul, the craft of a human being's touch ..." - David R. Hawkins