I am building my first fixed/single and the decision for either seting depends on your advise. I live in a very hilly place and I am planning to set my bicycle either 5.5, 5.1 or 4.8 gain ratios. The 5.5 cames out of 42 - 15 fixed gear, the 5.1 from 42 - 16 single speed and finally, the 4.8 comes out of a 42 - 18 single speed. Now, I am not afraid of climbs, but I am afraid of descends and I think that a 5.5 gain ratio is going to make my life dificult on a descend because is too slow. On the other hand I can use the fixed configuration on flat places confortably. For the single speed configurations, I can always rest on descends and let the bicycle go. So, please guys, what is the best combination for my needs?