I looking to get a fixed gear bike, but the one i want only offers 3 frame sizes. They offer a 50cm small frame, a 54cm medium frame & a large 58cm Frame. My Madone 6.9 is a 56 cm & fits me perfectly. So which frame would be a better fit for me the 54cm or the 58cm ?. The fit specialist at my local Trek store sayed he would rather see me get the 54cm over the 58cm. What are some educated opinions ?.