Take a look at your Soloist's aero seat post - I've seen the tops of the bolts coming up pretty high, almost into the cutout of a Specialized Toupe (almost the same saddle as a Ruby). It looks like the bolts could hit you when the saddle flexes. I didn't ask the man riding it if that ever happened...
So when considering different saddles, make sure the vertical clearance between rails and saddle is high enough, because all the posts your Soloist will accept have the same hardware on top.