In comparing the exact specs of both the 12-27 and 12-29, I'd go with the 12-29. They both have 12, 13, 14, 15, 16, 17, 19 and 21 sprockets and you'll benefit from the tighter spacing on the flats. The differences are at the far end of the cassette and, at that point, I think you'd benefit from a easier, rather than harder, gears when the road gets steep. Either way, I'd expect the shifting, even with the bigger jumps. Campy shifting is always so smooth IME. And remember that you won't have this cassette forever. If you end up wanting the tighter spacing, you can opt for that when you eventually replace the cassette. I'd err on the side of caution at the outset.