I'd take the 20" over the 24" all-day every day, especially if you're not a peasant and own a suppressor. My wife's 20" CTR .260 is the most accurate factory rifle I've ever owned.
It's a CTR (COMPACT Tactical Rifle).... if you go with the 24" pipe then it's just a TR... laffin...
Luckily they make a 6.5 CM in 20" guise as well, so the buyer has a few choices. Barrel length preferences are definitely going to depend on your needs and uses. I mostly use my RPR to shoot at the local long range, and at our range's PRS style shoots, that is also how I would use a 6.5CM CTR. In both of those situations, there are usually other shooters around, most of whom will not be using suppressors, so I have to wear ear pro any way you cut it. Because I'm wearing ear pro anyway, and the 6.5 isn't too loud out of my 24" barrel, I really don't usually bother using my suppressor at matches. This time of year especially, the wind up here in Wyoming is pretty ridiculous, and usually full value where I shoot, so I'll take the extra 75 fps to 100 fps from the 4 inches of extra barrel over a more compact rifle for my specific purpose. Hell, a few of the guys that were shooting .260's in our matches just went to 6mm Dashers with 28" barrels... That's a bit long for me, but 24" works out fine.
That said, if my situation were different such as I was able to shoot long distance on my own land or with one or two other people who were also using suppressors, or if I was shooting somewhere with less wind, then yeah I would probably be inclined take a shorter barrel and use a can all the time. I also love using a suppressor for hunting because I don't like to wear plugs while hunting, there's usually no on else with me, and the ringing after a shot is always a reminder that I just traded a little bit of my hearing for meat in the freezer... not a trade I'd like to make if I don't have to.
