My previous stable for road bikes was an s-works roubaix and tarmac. I’d run them with the exact same position by downsizing the roubaix frame to get a lower stack.
Both of these bikes were prior to specialized going aero for everything, so it was mostly about the different frame dynamics. I raced both and it was course dependent. We’ve got a local crit series on smooth roads and it was always the tarmac. Road races depended on the expected road surface. I raced the Roubaix for crit and road race at stage races included rough roads. I wouldn’t say either bike was generally faster, but the tarmac handled a bit “racier” and was maybe a half lb lighter. A bit more fun on a tight crit course. Roubaix was definitely smoother and more confident on rough roads and smoother = faster in my book.
I’m still a big fan of specialized, but my current stable is a Trek madone and Domane. I bought the madone because I wanted an aero bike and it was much better than the venge when I bought it a few years ago (I think they’ve improved the venge since then). The domane was bought as a gravel race bike since it takes 38mm tires, but it’s become my backup road bike as well and I just sold the roubaix. I looked at the new roubaix, but it didn’t have the tire clearance I was looking for and I just couldn’t get past the funky future shock. I work on my own stuff and I don’t need another proprietary suspension component that needs special service.