When I was shopping for a new bike last year, I was looking for a bike that had Di2 and disc brakes. I didn't consider the Supersix Evo because it was, by far, the cheapest bike out there that had the Di2/disc combo. I figure that it's the cheapest for a reason: the TA on the rear wheel being an obvious warning of cost cutting. What else have they skimped on that you can't see? You almost always get what you pay for.
I'll third or fourth the statements on the inadequacy of test rides. The BMC that I finally settled on felt much different after 2-3 months than it did, say, the first week I owned it. My bike shop will let you take a hour or so test ride, but that still won't let you know how the bike will ultimately feel to you. I suppose all you can do is rule out bikes that feel horrible right from the start.