I am thinking at this point of a few people that have the high HP kitfox's, called I believe the Cub Killer. I think the main purpose in their mind is to get off the ground faster and climb somewhat straight up. what their top speed really doesn't matter to them.
I personally have the 4 with the uls 100hp engine. along with the adjustable prop in flight and the fact that it is light, 650 dry. I can get some great take off's. Ya nothing like that 140+ wonder out there I'm sure, but it is fun and the aircraft handles very light with the power to weight ratio. Oh and I can fly 102kts all day long. My smooth ride is at 84kts which I do a lot for fun flying. 102kts I do to get to my play area faster. speed is important only because I have a busy schedule in my life and I only have so much time for play. can I put more horsepower on my plane, sure, but more HP cost money. sure I can do it, but I love the way it is now and I'm just going to leave it. I'm more interested in TBO at this point and I know the stock 912uls has a good one. I vote on my plane to leave it be and enjoy what I have.