I purchased a M4gery and a 24" Varmint (bull barrel) to do some prairie dog hunting last year and both worked great. I found myself favoring the M4 style for a few reasons; it is lighter, it has an adjustable stock, and I was using a 1x-4x scope (left in 4x post of the day). It was quicker in aquiring the targets. Since we didn't use shooting benches like a lot of doggie hunters do, I had to change the stock position for a few different shooting stances (Top of the truck, truck tailgate, truck hood, and on the ground). Also we were shooting pretty fast without a spotter, we scanned the ground in sweeping motions (4x) and as we saw the doggies, pop, pop. FLYER!!!
Tons of fun. I wasn't too interested in the long 300+ shots as there were just too many to pop up closer. It was more fun seeing the buggers fly at 50 yards!!!
Granted almost any rifle is good for Yotes, even the 17HMR is doing well in the yote hunting circles. So the power gained from a 20 to 24 incher isn't enough to matter in my opinion, and for that matter 14.5 to 16 all the way to 24 won't matter that much (again my opinion).