Yeah, huge top tube. That is the killer. My road bike has a 61 or 61.5cm tt. Was a pain in the rear to get them to make it. They (columbus) would not do it for warranty reasons, that was what I was told anyway?
My legs and upper body is in proportion, huge in both. I was 6'3" at 13 so I have never been "off the rack" that I can really remember anyway. At least with a BMX you get a long TT, stem and cranks and you are good to go.