the worst case stretch is from 120mm old 2x5 10 speeds to 135mm hybrid/mountain... thats a 1.5cm (15mm) stretch, which is 7.5mm on each side if you will. if you stick with road axles, its 120->130mm wihc is a 10mm/1cm stretch, 5cm per side. either of these will let you run 8/9/10 speed cassettes.