Rich,
I've sailed the Infusion the most, and have done a couple events on the C2. I don't think you could go wrong with either boat, and I'm pretty well convinced there is not much of a speed difference between the two. Personally, I like the layout on the Infusion slightly better than the C2, but that could just be because I have sailed the Infusion more.
I think the chord length of the C2 boards is slightly bigger than the Infusion boards, so that is a little more forgiving when downspeed or on a startline. That said, we have found the Infusion with the long boards is super fast in marginal single wire conditions. Either boat should work well, and the ergonomics that make me happy as a crew (adjustable traps, cunningham lead to trapeze, etc.) can be added to either boat.
That said, if I were going to buy a new boat, I would look very hard at the Falcon. The boat has been getting some good results down south this winter, and I really like the dealer support combo of Falcon Marine and Glaser Sails.