Beautiful bike! I'm a big Cannondale fan and went from around 218 to 190 in a couple months watching what I eat and riding 150-200 miles a week on my CAAD9.
Have you had a professional fit? I realize the Synapse is more of a comfort bike and know you worked with the shop owner a lot but there appears to be little to no bar-to-seat drop and the frame appears really compact for a 5'10" rider.
I have about 11cm of drop on my CAAD9 and I'm 6'1" tall. Totally different geometries between our bikes but I'm wondering if you're giving up some power with that fit. I had a retul fit after putting on 2000 miles on my CAAD9 and it made a HUGE difference to my comfort and power.
Again, without even seeing you on the bike it might be a silly observation.
Continued success, sir!