Ok, so you want to go to a Giant store pretending to be a customer just to size a a Defy on the chance the Gravity will be the same size? How about trying the Defy and if you like it, buy it?

I wouldn't buy a bike off the internet unless I really knew what I was doing. the bikes direct bike looks impressive on paper, I wouldn't buy it unless I knew for sure it would fit, and I was confident enough to competently assemble the bike myself.