Actually, the '05 650 is a different bike than the '04 600 - unlike the '05 1200, which is relatively unchanged from the '01.
Bandit 600 up thru 1999 is a 1st Generation
Bandit 600 2000-2004 is a 2nd Generation
Bandit 650 2005-2006 is a 3rd Generation
Bandit 1200 up thru 2000 is a 1st Generation
Bandit 1200 2001-2005 is a 2nd Generation
Bandit 1200 2006 is a 3rd Generation
Some of the changes in the 3G bikes include all more cc's on the 650, new tank, seat, bodywork, airbox, and instruments. I know the 1200's also got different brakes (with ABS option), not sure about the 650 though. I doubt a 600 air filter will work and I'd be VERY careful on any accessory purchase.