I’m not sure how much it helps, but I owned older generations of both bikes. I had a 2014 Roubaix (my first road bike) and a 2017 Synapse. Both models have been revamped since then.
The Roubaix was instantly comfortable and muted the road like nothing else. But it was also incredibly flexy, which I didn’t realize till I got the Synapse.
The Synapse was just as comfortable as the Roubaix (similar geometry) but so much stiffer, and therefore much faster. I felt a bit more road buzz with the Synapse, but it was worth it because it rolled along so much quicker. I’ve heard that the new Synapse is both faster and more comfortable from folks I know who had both, but I can’t speak on that from personal experience.
As for the BB30, I’ve had 4 different Cannondales (Synapse, CAADX, CAAD12, and SuperSix Evo) and I’ve never had a single issue with a creaking BB. My CAADX has over 10k miles on it and it has never give me an issue, and I’ve ridden that bike through some truly gnarly conditions. That is my all-road, gravel road, mountain bike trail, ride-it-in-the-rain, give-it-hell bike.
I changed the bottom bracket one time, and that wasn’t even out of necessity. I was in between road bikes, so it was my main ride at the time. I have a Kogel ceramic CX bottom bracket, so I put it in there. But zero issues either way.