Definitely consider the 650c wheels. I've been coveting the Cervelo RS and one of the reasons is precisely because it has 650c wheels-and great geometry as a result-in my size (XS). If I bought a tri bike I would definitely get one with 650c wheels given my height.

That being said, my main ride is a 49cm unisex Merlin with 700c wheels and man oh man do I love my that bike!