I want to think it's 1" over stock. Look at the wiper tip on the drivers side as it goes perfectly vertical. Distance from tip to windshield gasket is your length limit. I don't believe there is a problem on the passenger side when in the park position. (Edit: ahh, 1" on either end=2" longer, so that's what I was thinking...I stand corrected)
I'd like to increase travel a bit so that park was lower, and at full wipe, it nearly contacts the edge of the windshield. But I believe that would have to be done through the motor/linkage at the motor.