Yes, it will void the warranty!
Power...yes, I've seen first hand how well the SDI responds to the Cudney Pistons and Head. My buddy installed them on his '05 SDI and it made huge mid-range difference. He had roughly 5 miles on his sled (post kit installation) and would walk away from my stock '05 SDI in the mid-range....and he stated that he never pinned it. I think he has roughly $1K in Mod parts...Cudney primary clutch kit, Pistons and Head, Hyperlite secondary clutch. He's running a 121X1.75 Camoplast.
I WILL BUY A CLUTCH KIT ON MONDAY! DYNAMO^JOE...where are you?
I say clutch it first! Ride it and then decide if you want to Mod the motor, simply because I think it's the biggest bang for the buck and will most likely NOT void your warranty. Also...I don't think too many people are Modding out their SDI motors.