Haha! I never thought picking out a Kukri would be so detailed. Thank you all for helping me with the decision.
I'm torn yet again, lol. I will probably start out with an 18", and most likely will end up buying the 16.5" as my second HI purchase. Although, from her email, Auntie said they only have one CAK in stock and it is 19.5". That might be a little too big for me.
This is like horse people talking about racehorses, or dog people discussing dog breeds. There are many opinions and many options. After reading your comment about having a job where you swung 3-5 lb sledges all day, I figure you can handle an 18" CAK with no trouble, but that still doesn't mean it's the best choice. Depends on what kind of use you anticipate. If it's mostly chopping down small trees or thick branches, then an 18" CAK is probably best, for its heavy chopping power. However, if most of the use will be less heavy, then the 16.5" CAK is probably best. It is still a massive, bulletproof blade that can do heavy work, just will take longer to build that log cabin.
If you end up with an M43, I'd go for the 18" because an M43 is not quite a dedicated chopper like the CAK, more of a combination tool and weapon by design.
As someone else mentioned above, weight is at least as important as length, and that can vary substantially even for the same model and length. Some kamis tend to make very heavy blades, though not always. Sher has made some of the heaviest blades I have, and also a few of the lightest. He's that good. Vim tends to go heavy on most of his blades.
Someone also mentioned handle girth. The kamis often make the handle girth proportional to the size and weight of the blade. A 19.5" CAK might have a handle too thick for you to hold even if the weight is acceptable -- unless you have large hands.
One more consideration: A person who uses a khukuri a lot usually has both heavy and lighter tasks. If you are going to end up with two blades, they shouldn't be as similar as an 18" CAK and a 16.5" CAK. In that case, if you start with an 18" CAK, I suggest that your second blade be a KLVUK, which often run around 20 oz and can take care of the light-to-medium tasks, also easier to carry if you do a lot of hiking, and much less expensive. Or you might go with a 15" CAK for a second blade, if and when that becomes available.
As for your first choice, since you are torn between a 16.5" CAK and an 18" CAK, I suggest that you tell Yangdu that you will take whichever blade in that range comes along first.
Some might disagree with this, but that's what makes horseracing. Good luck.