Really the best advice for someone who really likes to ride (and is willing to sell the wife and kids to finance the hobby )

If you usually do day-long rides .... can you spend six hours or more hours in a full bend enjoyably? I know my lower back and the muscles between my trapezius at the base of my neck start hurting after a couple hours all the way down. If you are planning to do a lot of epic rides, I'd consider a more relaxed-geometry bike, but you know yourself best.

These two bikes are at the far ends of the spectrum ... but as rms13 points out, people used to do all-day rides with racy geometry bikes. (Of course, it was their pain and suffering which prompted the "endurance bike" movement. ) But the bikes were designed to do different things. If you do not plan to race, why by the race bike?

Also, is it the full-bent position, the low bars, the quick handling which comes from steeper head tube and shorter wheelbase ... what part of 'fun, racy geometry" appeals to you?

You could probably get the bars on the Synapse as far below the saddle as the Super Six, and by swapping the stem change it to ultra-comfort mode when you planned to go really long distances (dtrain confimms this.) If it is twitchy handling you like, you could probably do the same on the Super Six.

I still say, ride both some more, and ride some other bikes. If no one bike strongly recommends itself, you will probably spend a lot of time wondering if you made the right choice. Keep testing these two and others until one bike or another decides for you.

If you are only going to buy one bike for the next few years, spend a few extra days making sure it is the one.