I generally run a 39/25 for most rides. When I went to the Alps for the first time last year I went with a 39/27 and took some time to acclimatise to the riding! Alp D'Huez was an absolute suffer fest...
I wasnt in the best shape and continue to get stronger with each month of cycling. When I return to the Alps this year I will accept my limitations and be taking a compact. Now that I know how small a change the 38 Vs the 39 is I wont bother for sportive events here I will just ride the 27 cassette.
Thanks