For a 660 ? My money'd be on suspension after gettin that all setup. I got as far as the Pipe, intake, and stage 1 cam ... like you said, next comes that P&P, HC piston, (and maybe a small bore... :grin_nod: ) ...
But yeah, I'd would look into the suspension. I got better shocks up front and +2 arms - it's amazing how much more stable it is. Widening out the front really let me use a lot more of the bike after the intake/exhaust mods.My next mods personally will be an adjustable axle, and extended swinger to improve the handling more. I feel a lot better on a wide 660, the center of gravity is so damn high on 'em. Plus, if you get a cam/piston setup (especially if you bore it) with a P&P, you'll want that extended swinger to keep your front end down.