in my experience with XP ownership I focused more on acceleration and mid-range than I did top end because at the end of the day, the top end difference between 55-60 really wasn't significant to me, but how quickly I got there was more of a priority, especially how quickly I popped from 25-50 when I pegged the throttle.
Prok Flame arrestors, jetted stock carbs, factory spec 1, EWCI, jetted waterbox, swirl prop was my favorite setup. I still ran under 60, usually 58ish, but the holeshot and midrange were so much fun.
I was never a fan of the aftermarket sponson's, I didn't like turning on rails, got tossed quite a few times and it got annoying and occasionally painful now that i'm in my mid 40's, so I kept the stockers on my personal ski.