If you want to get the most out of your 80 rotax on your model 4, put the prop that I have for sale on it and you will get up to that 110mph. I know, I had it on my 80 model 4 and it did move right along. I have the IVO patriot ultra light prop in excellant condition for 700 dollars, it's yours if you want it. You pay the shipping.
I did switch to the rotax 100 and I might have gained 3mph on the top end, the biggest change is the take off. I ended up putting on the medium IVO that's why the old one is for sale. It's is a straight across switch out, no suprises. Same engine, just more juice.