I just replaced (double ring, 53/39) my Ultegra 12-25 (10 speed) on two of my road bicycles with 12-27, about 2 weeks ago. Now, 350 miles later, no complaints. I never use the last (largest, 23&25) two cogs so on the flats you won't notice any difference since you will be using the first (smallest) 8. On the hills the 24&27 is more help than 23&25. It is nothing like a compact or a triple but better than 23&25. If I had a Campagnolo 10 speed I would have chosen 13-29 for even better spread of hill gears. I dont use 12 and rarely use 13 because I do not fly down-hill and I am no sprinter either so really 12 is not needed for me either.