BBtI's data for 18" barrels doesn't refute the 20" and 22" barrel data other folks have posted elsewhere on the net. Some 240gr 44 Mag loadings are still gaining velocity from a 22" over a 20" barrel with some loads tested.
Comparing a 20" rifle to a completely different 24" rifle, to a completely different 18" rifle will get you nowhere. Every barrel is an island. We discuss that
daily on this forum.
Even so...
The advantage gained from keeping the 24" barrel is negligible.
No animal is going to tell the difference from 50 fps lost. (See what I did there?

)
If a 24" barrel makes sense where you hunt, then have at it.
For where and what I hunt, the only time a .44 Mag rifle makes sense is when it's light and very compact (18" or shorter barrel).
If ~1,600 fps with 240 grains of lead, isn't good enough, then I shouldn't be asking .44 Mag to do the job, anyway.
And that's not even taking into account the fact that I have two .444 Marlins sitting here, as well. One of them, gun gods forbid(!), even has a 19" barrel that keeps the cartridge from attaining max velocity!

(2,300 fps vs 2,400 fps, but 5 inches shorter and a little lighter? Yep, that's a sacrifice I'm willing to make.)