If your friend has had an opportunity to handle your CAK, and if he still wants something bigger and heavier, then he should go for an 18" M43. There is no one-size-fits-all for these blades. Some people are a lot bigger, stronger and fitter than others and can handle a blade that might be too heavy for most people. Some are gluttons for punishment and just want the biggest, heaviest blade that they can fit in the back of their pickup truck without blowing a tire.
It also depends on the expected usage. A good bit of advice is to pick a blade that is best suited (for the physical capabilities of the owner) to the main use that he expects. It might end up being overly heavy for self-defense, but to fend off the occasional attacker any sharp piece of steel will work in a pinch. It might end up being too lightweight to chop down trees and build a log cabin, but how often do most people do that? There's always an axe or chainsaw that can be deployed for a once-in-a-while project.
If your friend does not live near you and has not had a chance to handle your CAK for purposes of comparison, he might be subject to a common misconception. HI blades are enormously strong, thick and heavy compared to most blades, and newcomers are likely to buy a first khukuri that is too heavy for them and will end up as a display piece. Or it could serve as healthy exercise and help the owner to become stronger in the wrist and forearm. That's what happened with my first khukuri.