I've been doing some searching on this and finding a lot of conflicting information. 99% of my riding is on pavement and 95% of that pavement is smooth. There are the occasional bumps and gravel on the road from repaired pot-holes, etc. I've found my stock 25c tires are pretty comfortable with my carbon frame but I know my frame does support 28c tires.
I am going to ride these 25c's until they're wore out or otherwise not in good shape anymore but when the time comes to replace them I'm thinking about going with 28c just for a little more cushion/contact area especially considering some of the pavement I ride isn't as smooth as it could be.
I'm mostly looking for first-hand experiences from people that have gone from 25 to 28 or 28 to 25 - was the change noticeable/large or minor?
I do have a Trek hybrid that rocks 35c's that has a pretty plush ride and I use it when I'm going on roads/trails that are really poorly maintained so I'm not looking to make my road-bike into a comfort or hybrid bike but just looking to optimize it a bit for the riding I do. I did buy the Synapse because it was capable of mounting the 28c's just in case I decided to go that route but was unsure at the time as I had never been on 25c's before .