I was just in the same position as you are. I liked the ride SPi's. But heard a lot of good things about the Union forces. The rides are $40 more, but I liked their wedgie foot beds and gel toe caps. After some research and listening to what others had to say, I decided to order the Unions. From what others say, the rides are a stiffer binding.
So I guess you could add Union's bindings to your list. But sorry I haven't been able to try either bindings out to let you know how they feel.