A surly is a touring bike. I do not know if you have any intention of touring on it? 99% of bicycle tourists are riding on too big a bike. They simply neglect to consider that when they put things on the rear rack, they have to get use to putting their foot over the top tube. (to mount). So a bike with a lower top tube (even a ladies type of frame) has advantages, while a high top tube actually has no advantages. Another basic rule of thumb is that you should have more seat post showing than the size of the head tube.