"he told me I needed a 62.8 cm frame" As you apparently know not all frames are measured the same and not all frames are the same geometry. When someone says they need an "x" sized frame you still don't have enough information on which to make a good purchase decision. I'm guessing the guy at the bike shop measured your inseam and and calculated frame size based on that. Educate yourself a little on basic frame fitting. Do a search on this site on "bike fit" "frame size" etc. As long as you don't end up with excessive saddle to bar drop and you don't need a crazy long stem then the frame you select is probably not too small.