Jesse - I test drove the LSV with both the 340 hp Monsoon and the 400 hp Hammerhead. I bought the Hammerhead. I alwasy subscribe to the theory that more is better, but in driving them the difference was so noticeable that I wanted the HH.
With that said, I did not want the 8.1. Although on a new boat the difference was nto much more than the HH, maybe another 1500, but I knew I did not need it. The 8.1 is more engine that necessary for these. It would change the riding dynamic of the boat by placing more weight in the rear. Great for boarding, but bad for trailering and generally riding around.
BTW - the HH uses 89 octane, so not premium, but not regular either. Since there is no 89 on the lake (for that matter, they don't sell 87 on mine) then it runs on premium.