Those 439mm chainstays should work for most folks. My chainstays range from 450-470mm and my shoes are size 51. The only heel-strike issue I have is with the shortest chainstays if I choose to use my largest panniers and wear running shoes with a big padded heel. If you're wearing normal cycling shoes and don't have clown feet like me, you shouldn't have any problems unless your bags have a particularly rounded shape.