BR505 disc vs Ultegra 6800 caliper I'm looking to get a built bike with either Shimano BR505 disc brakes or Ultegra 6800 caliper brakes. The bikes I'm looking at basically have the same frame and components. They both have the same frame, it's just that one is for caliper and the other is for disc brakes. They both have straight Ultegra 6800 components except for the one with the disc brakes, ST-BR505 shifters and BR-RS505 disc brakes.

I've ridden a bike with Ultegra 6800 components and found that the shifting was really smooth and the same goes with the braking. From what I've read, the BR505 is 105-level. I haven't really tried 105s yet, (I've tried a Deore SL-M591 mated to a 105 5700 rear derailleur; does that count? Although I found it not as smooth as the Ultegra 6800.) so I'm not sure how the shifting and braking would feel on the BR505s.

Would there be a noticeable difference in shifting? And, I guess, the more important question, would there be a significant difference in braking power between the two brake sets? The price is the same for both bikes so that's why I'm really having trouble deciding on which to get.



PS
I plan on racing/exercising with this bike. Don't really plan on commuting with it since I already have a commuter.

The bikes are Giant TCR Advanced 1 and TCR Advanced 1 Disc if that helps.
They're not entirely the same bike (despite the model names). You have to engineer a disc brake fork to be reasonably stronger in some ways than a rim brake fork. 

You probably won't notice a difference in shifting or ergonomics once you get past a certain point (for a lot of people, I'd say this is Tiagra/105; however the psychology of having an ultegra shifter or whatever will make things feel smoother even if they aren't noticably smoother, for some people). The braking will be stronger with the disc brakes, and easier to stop if you ride in wet weather. On the other hand, repairing rim brakes just requires a few hex keys and a few minutes and anyone can do it (vs a hydraulic system).

Really though, you have to try both bikes in the context you'll use them. You may like one better than the other. You also have to think about how teh disc brake and rim brake bikes cost the same -- disc brifters+brakes are more expensive than their rim counterparts, along with the cost of the wheels and stuff. So, where is the rest of the stuff being cut down in price?