I don't see any reason whatsoever why you wouldn't be happy with either one, and that you would have to upgrade anything is a pile of bull. Sure, there's no end to the money that can be spent, but is it really necessary? I have to admit I have what was a fairly expensive bike when I got it (10 years ago), but really, I was just as happy riding a cheaper entry-level Peugeot I had before that. I'm not personally sold on whether a carbon-fibre plastic frame is much of an improvement. I like metal and I like the Roubaix model. If I had to buy a new bike, I think that's what I would go for if I couldn't afford a new lugged steel frame, but I think I would be more than satisfied with the plain one rather than the carbon frame. I had 105 components once, and as a very experienced non-racing road rider, I don't see why anyone would actually need any better than that.