Supersix Evo 105 5 2015 Vs Synapse Carbon 105 2015?

Hey

I'm looking for a secondary bike (primary one being a Cervelo S3 2014 6800) for:
- commuting to work (with average road quality)
- trips (plane)
- races where the conditions aren't ideal for the Cervelo (heavy rain, dirt, etc)

With my racing team, I now have a sponsorship with Cannondale so the intuitive options are:
- SuperSix Evo 5 2015
- Synapse Carbon 2015

Since it's a secondary bike, and since the 105 5800 components are well rated, I would probably opt for this gruppo.

My dilemmas:
- The Synapse is a 160$ extra compared to the Evo
- I would sometimes race it, let's say 10% of the time
- My commuting to work also represents 75% of my training program, so I need a bike that won't cause too much adaptation issue when racing my Cervelo S3

- On the other hand, the roads here are pretty bad so I wouldn't want to suffer injuries from using a very stiff bike when commuting
- Also, am I right when saying that under heavy rain, the Synapse would be slightly more stable than the Evo due to road absorption?

I also put the CAAD10 in the options just in case, but please note that the sponsorship isn't as interesting, making it only 240$ cheaper than the Evo.

Thanks!