Really, it comes down to usage. If you want ballistics that are solid out past 5 or 600 yards, I do not like anything where you are using a preset curve,, so that puts the 2k out for me. And if you take ballistics off the table, go 2400...newer, more horsepower.
However, If you want ballistics, but don't care to shoot past 500 or so, my experience with the presets is that they were sufficient for game to that distance, maybe a bit further. YMWV depending on just how close your load runs to one of the curves. In that case, the 2k will work.
As far as ranging horsepower, 2400 should win that one. I don't have one, but folks I know that do and in talking with Leica, it should win that one. Of course, there are no ballistics functions (other than angle modified) with the 2400.
And if you want ballistics that will take a custom curve, and so will be accurate out farther, you need to look at a 2700 or higher. Sadly, those all start at like 899, and Leica is pretty strict about MAP. There are rare discount programs, you might reach out to Doug at Cameraland and see if he is aware of any upcoming Leica sales events, but they are pretty rare.
That's pretty much how I see the Leica CRF lineup and how I'd make a decision on which Leica to buy.
