"Sorry, I've got to agree with Russ on this one. Using www.sheldonbrown.com/gears
and assuming a "standard" 11-34 cassette, and calculating the speed at 60 rpm (slower than I'd like to climb, but sometimes necessary), I fly up the hill at 3.4 mph using the 24 tooth chainring. Compare that to crawling up the same hill with a 22. (/sarcasm off) Yes, you're talking about one extra gear. But I'd give up that lower gear before I'd compromise shifting. I don't know of a way to reliably shift to a 22 chainring using STI shifters, and it's critically important to be certain you can use that lowest gear when you hit the nasty hills. Besides, we're approaching the speed at which I can walk a loaded touring bike uphill (2.7 mph, verified more times than I want to admit!)."
Compromising shifting is not true, with well planned gear ratios. As mentioned, I do not use or recommend STI shifters for touring (reason given). Walking a hill for me would be very rare (maybe you need lower gears). As I stated, I think 24T is fine for a target, but as I also stated, lower is better, particularly for someone with limited experience as the person who started this thread. Percentage makes a difference, and it is not to palmed off with comment couple of teeth difference doesn't make a difference for lowest gear. I have experienced the difference using 24T low and 22T low over many thousands of miles.
That experience caused me to remove crank with 24T low on new bike I am building to substitute a crank with 22T low at significant expense.