Forget the science of it all and go with feel and experience! Damn some number crunching anyway, half of it is just plain voodoo (or is that shocks and springs, hhhmmmm? but anyway, back to tires)
Tire size is somewhat subjective. I've seen identical brand and model tires of the same size be different diameters, right off the shelf. Tire size will vary depending on the amount of pressure you run. Brand new tread as opposed to well worn tread can make 1" worth of difference. For this reason it can be somewhat hard to compare a 24 to a 23, or a 22 to 23, etc. You'll see noticeable differences from 24 to 22, 25 to 22, etc. (maybe).
Top end speed? Hmmmmmmm? That's a good one. Discounting all the genital insecurities out there, who really ever gets to actually use top end speed other than those who can run in WIDE OPEN terrain? You might jump up to your top speed momentarily but are usually on and off the throttle constantly if you trail ride. In most all trail situations, and many fairly open area riding, you should be much more concerned about handling than top end speed. Cornering without tipping or rolling, has as much to do and more with suspension than tires, though tires are a large contributing factor. Tread pattern is as important as overall diameter. A large tire might not roll in a corner at all if the tread pattern will allow for a good break away when wanting to power slide. And conversely, if a pattern will bite immediately and keep a slide from starting at all, you may never break loose then hook, causing a roll over. I've found that tread patterns in the front are about as important as in the rear. In certain situations you want the front tires to go EXACTLY where you point and other times you love to have some drift or understeer. Ply rating can assist or prevent roll in corners, front or rear, based on how stiff the sidewalls are. A 6-ply rated 24" tire might have less roll than a 2 or 4-ply rated 22" tire. This could go on and on and is only one individuals opinion.
For what I've experienced:
I ran 25 x 12 - 10's in the rear for a very long time. What I experienced was good top speed (which I never needed realistically), a tendency to roll a bit in turns, good ground clearance, and a shitload of bounce!!! The rounded shape and overall size helped in getting over a lot of rock structures but the disadvantages weren't worth it.
I tried 23 inch tires and then went to 22s. The 22 worked best for me overall. I came out of the hole better, could break it in a corner better, and experience much less roll in cornering. I also have to admit that suspension changes were also taking place during the tire changes. Tread patterns differed in the 22 inch sizes from an aggressive mud-type tread to a mx type tread.
In the front I've gone from 21 to 22 and then to 23 inch tires. The flat profile tires were great for hooking when wanted and going exactly where I steered. The rounded profile was better for overall flexibility in handling control. The 23 inch tires in the front seemed better for me in overall handling.
What I ended up with and liking the beset was 22 x 11 - 10 in rear (489 type pattern) and 23 x 7 - 10 in the front with a rounded straight tread pattern. Specifically it was Titan 489XC (6-ply) in rear and Pure Sports Bandits XC (6-ply) in front.
Have a nice day!