I went from 170 to 172.5 because the new bike was speced that way. I ride with my saddle 2.5cm higher, but then that chages body position in regards to handlebar height and stem length. Everything is connected to everything else. I tweaked a lot before getting things the way I wnated them. I'm not sure that there is any real advantage in longer cranks. In theroy, of course, but I often cannot feel theoretical differences.