I test rode a Roubaix (and 3 other bikes) before buying (through eBay!)
I found the Roubaix was noticeably smoother.
My Roubaix is a 2007 triple. It's got about 20K miles, the crank, brakes, and shifters have all been replaced with Ultegra and I had to replace the wheels (take offs from a 2013 $5K Roubaix). I am 6'1" and 230#