Originally Posted by Stannian

If you are looking for a more aggressive geometry, size down, maybe longer stem. The handlebars will be lower compared to the seat than the larger model. Size up if you are looking for a more upright seating position at a more reasonable pace. Or get the one that just feels better. That should be the ultimate deciding factor. For a bike like that, an hour test ride should not be unreasonable for the shop to allow.