That's kind of like asking "how big a wake can one of these performance boats put out if you repropped them?" The hulls are designed completely differently. I know some ogf the bigger Xstars and a few others are running the 496/8.1L but the hulls are designed for one thing.....big, smooth, shapped wakes. You could re prop but that really won't give you much. My guess is 55 to 60 mph but it wouldn't be the best ride and who knows how they would handle at that speed, not to mention you'd lose your wakeboarding ability.
I think if speed is your most important priority get a performance boat and add a tower and maybe tabs. With a few phat sacks they can be made to throw out a decent wake, nothing as nice as a wakeboarding boat but I think it is easier to get a performance boat to act like a wakeboard boat than it is to get a wakeboard boat to act like a performance boat.
Just my $.02,
Chris