I used a Novak Rooster ESC I got for cheap on eBay on the Cranberry I built. It worked fine, just had to make sure it stayed dry, so I mounted it up high in the hull under the cabin.

Like Kmot said, the stock setup (Mabuchi 550 direct drive to the kit's 3-blade prop) moves that boat along nicely for scale speed. If you wanted to put a Mabuchi 555 motor in there it'll probably get a longer run time at slightly lower RPMs. That's what I put in the Cranberry I built, but those motors don't seem to be quite as easy to come across. Last time I found a 555, I pulled it from a copier that my work was throwing away.