I'm in the same boat with you, Andy, I'm waiting on my new 5.1 from the presale. But I can tell you that the previous 5.1 also felt like a much bigger knife than the RMD. And the new version is a bit longer yet. But you're right, you will have to handle both to see.
I love the way the RMD carries flat against my side, in part due to the flat sides of the scales. It is a very low profile knife in that way.