Depends on the tire usually. With 35 series tires on some 19s, I'd say leave it at 35 or a little higher. What does the max say on the tire?
Edit: You should leave the stockers on the car while you dyno it...You're most likely going to lose some hp through the larger wheels, if you want bragging rights, just dyno with the stockers....or hell, dyno with both setups to see for yourself.
