What the shop might mean is that a 56 road bike and a 56 track bike are waaaay different. The difference is in the higher bottom bracket. Most, not all, of the time you will be more comfortable on a 2mm smaller, numerically, TRACK bike. Now this does NOT include a bike with road geometry set-up as a singlespeed. i.e. Jamis Sputkik vs. Fuji Track Pro. The track bike 56 will have a higher top tube than the 56 road bike. Ride both and decide for yourself. As long as you have a comfortable distance over the top tube and your junk isn't resting on it you'll be fine.