Chris.. I own a 223 WSSM. what does not do this rifle justice is the 22 " pencil thin barrel and the 1:10 twist. If I could have a 26" BBL, 1:14 twist and the barrel has a 1" muzzle then I would say this rifle is just about perfect.
if you want my 2 cents worth. use the 22-250 or the 223WSSM. the 1:12 twist would be perfect for both. a friend has a 1:12 twist on his 22-250 and its a rock solid tack driving machine with 40 to 55 grain soft points and V-max slugs.
now my 223WSSM will blow the 22-250 out of the water if you reload. I can attain 4,300 FPS with a 40 grain V-max, Varget, and magnum primers. also the brass has to be annealed every time you reload. also you should match prep your brass as I have done it makes the whole rifle shoot better. the longevity of the barrel is that of a 220 Swift. about 2,000 to 2,500 rounds. my personal win M-70 Super Coyote will sink any prairie dog at 100 yards or less. after that the 1:10 twist spins the light slugs too fast and they destabilize on me. I am relagated to heavy slugs. 65 Grains and above.. but I can say I can stabilize a 75 A-max at 3250 FPS (starting load by the way) if you want a long range tack driver.. the 223 WSSM is the way to go. if you want an all around flat shooting tack driver the 223 WSSM is the way to go.. or if you want to find ammo everywhere.. 22-250 is the only way to go. in my mind the 22-250 is superior the the 223WSSM in longevity of barrels. I would not turn down a 22-250.. I stumbled onto a really smoking hot deal on my 223WSSM... that is the only reason I own it.. I would prefer the 22-250.. lower pressures, universally able to get factory ammo, and is one of the more inherently accurate cartridges.
in my mind's eye, both are great cartridges. I have everything to make smoking flat shooting cartridges.... but, I have to reload my own and I have to have my barrel replaced to shoot light slugs. this was and will be a varmint killer/predator rifle. once I am done with it.. it will be one. right now its a light packable deer gun.
if you go with the 223 WSSM.. you will not be disappointed. if you go with the 22-250 (non Improved) you will not be disappointed. flip a coin.. its going to be a winner either way.
Fred the gunsmith