If you really want to compare sizes between brands as you describe, you would need to be able to compare key measurements between bikes. Top tube length, seat tube angles, head tube length, and on CX bikes specifically bottom bracket drop vary considerably between brands. Some still use an "old" cyclocross style of higher bottom brackets, while many have lowered it to be similar to a road bike.

A higher BB will leave you sitting higher on the bike and often have you bent over a little more, all else equal. Trying to find something sized as a 63 will limit your choices greatly. Really though, you're just talking about adding about 10cm to a stem. It's not as big of a deal as some make it out to be, and those of us at the top end of the size spectrum just don't have a choice but to get over it.

I'm 6'4" and ride bikes labelled as 58/60/61/63... depending on the brand and how I want to fit on that style of bike. For example, I have a 58 Cannondale cross bike because they run a size big, and a 61 Specialized because they don't, and there's a huge size drop to a 58.