I own both a caad and carbon synapse and have ridden the supersix (not evo). They are similar but different. How's that for useful

Kind of depends what you are looking for. I haven't analyzed the prices but I don't think the Synapse is the budget bike in the line by any means although they don't make an "evo" model... yet. They do have alloy and carbon models so I guess the alloy model is the better price option.

I think to summarize the differences, if you want a snappy, more agressive ride the caad/supersix line is it. If you want a somewhat relaxed position and a bit more stability then a synapse is a good choice. That said, the synapse is no slouch and you can ride it hard and fast and the caad/supersix is certainly not harsh nor overly twitchy. Best to just ride them and see which feels more like what you want.