Just FYI - cyclocross bikes have a shorter seat tube (which is what is listed as the "size" for bikes) than road bikes, because the bottom bracket is higher - so indeed you probably would need a 42 in the CrossCheck if you normally ride a 48 in a road bike.

The attitude from the bike shop I don't understand..... maybe you don't "need" a steel bike - heck, you probably don't "need" another bike at all, much in life we don't truly need, but you *want* a steel bike.... they should be willing to sell you what you want...