Help with this bike

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I am looking at a Schwinn Road/Cross bike and am having trouble deciding the size. I am 6' 4" with a 33 1/2 inseam. I have shorter legs and a long upperbody. I was looking at this bike to start with, but not knowing about sizes I need help.

I went to wrenchscience.com and did it the best I could and got a frame size of 56cm (a little under 22"). I had the guy at the bike shop measure the schwinn (they only have large left) and it was 21". Now i dont know how big the XL is due to the fact they dont have anymore in stock and they can not order me one unless its online. I dont see the problem with it being slighly shorter but is it a problem in the long run if i get a slightly smaller size? When im at the store what should i look for other then the 1-2inch when standing on the ground. Whats the best way to decided (if there is any way to) if its going to stay comfortable for a long ride not just the test ride?


http://www.performancebike.com/shop/profile.cfm?SKU=24468&subcategory_ID=3040
That is the bike.

Thanks for any help.

try this link and see if its any help

http://www.schwinnbike.com/products/bikes_detail.php?id=747