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.