Interesting question. I haven't yet had the opportunity to try throwing the two side-by-side with the same surface prep, but I did have a polished Ultimate a while back, so I can offer an educated guess. Even with polish, the Ultimate will want to start up sooner and get into a roll in the back. So I'd expect that, while the overall hook would be equivalent, the Impulse would be a few feet longer than the Ultimate, and a bit stronger at the break.
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...formerly "The Curse of Dusty," and "Poöter Boöf" before that...