I've got a '14 synapse hi-mod and the new supersix hi-mod. Supersix is equally, if not more so, compliant. Only plus for the synapse is slightly more relaxed manners if that's your thing. I broke my back so wanted a taller head tube but managed to get most of my flexibility back so ride the supersix except for winter. You can fit 30's in either frame also so that's a wash.
Next seasons synapse looks good though. Less swoopy, lighter fork like the supersix, recessed seatpost mount like the superx and mud guard mounts if that's your thing as well as the mild aero shaping of the downtube.
Bottom line between the two really boils down to geometry and road feel. Neither lacks for tyre size or compliance. Ones just a bit taller and steadier, the other is a bit more agile and aggressive.
I'll pitch in. Having ridden both a '14 Synapse (non-hi-mod) and currently on a 2016 Evo Hi-mod I can say the evo is just as compliant over most paved road conditions. No experience on dirt or gravel but based on handling, the Synapse would probably be better for those surfaces. For road though, I would say hands down the new Evo Hi-mod is amazing! I think if paved roads are your main riding and you can get comfortable with Evo geometry, that would be my vote. Otherwise the Synapse is still and awesome bike, just not as nible or light. Interested to see what they do with the Synapse re-design...