I don't think you missed much if anything. The difference is probably mostly in my almost superhuman ability to split hairs...
The case is shortened slightly and blown out. Pretty much a 300HAM'R necked down to 6mm with a 40 instead of the 30 degree shoulder of the HAM'R. "Ackley-ized" like you pointed out.
Supposedly it has a -bit- more case capacity than the 6x45 due to being blown out, even though it's shorter. I should have clarified "heavier" bullets. I'm thinking 95-103 gainers might fit and work a little better in AR mags with their length constraints than with the 6x45, but I don't have any experience with either of them. If it was a bolt rifle with a longer magazine, any difference there might be would probably all but disappear.