V2 has the same piston diameter(25mm).
About saints - I want to try it, but as long as shimano are a retarded company (why to end production of such an awesome and successful product?) I don't really see any capability to try them (I'm too lazy to order levers+calipers separately and building it up).
I don't get one thing: why no one uses 4-cylinder hopes in street-trials? M4/E4 are pretty light V4 are crazy powerful and all this with better modulation than 2-cylinder ones.