I've got a 42/16 that's about 70 inches, and a 48/18 that's about 71. Given they produce nearly the same gear inches, is there any advantage to running one vs the other? I'm running single speed, not fixed. I'd like to pick up some freewheel cogs with one and two less teeth to get in the neighborhood of 75 and 80 inches respectively, but don't know which chain ring I should stick with. Thanks.