RE: Aquacraft Super-Vee 27 Nitro.
We being my son and I, tested a lot of props on the boat. The negine swung bigger ones that I thought that it would but after breaking a connecting rod I was worried that it could have been a result of trying to turn those over. The 40 x 57/3 should be fine but one thing that I did notice that the handing wasn't the same going big. The boat seemed to favor smaller props.
As far as the fuel goes, you're going to run it on the rich side for a while anyway so that really shouldn't do any damage. It will also give you a more forgiving needle.