"The crutch of the heavier round"
??
Or crutch of ligher rifle/lighter ammo/more shots/lower recoil with the 223?
Sorry. Even with an MOA rifle you (especially under stress) may not be able to hit the exact portion of the heart ventricle you wish to aim at, and even if you could you would have to know which phase of heart-beat your target is in.
223 in combat: Probably powerful enough, even a hit of quality that insufficient to put venison on the table may be enough for your target to decide to lie down play dead and wait for his trip home/purple heart equivalent.
However, I don't think you should sell your gun. Any new gun can have bugs in it, if (I assume) your 223 works keep it at LEAST until you find out your new baby works okay; but preferably forever. Even "postbans" will get more expensive after subsequent legislation (remember even prebans are crippled M16s). And rapid-firing a zero-recoil AR15 (despite the fact that one good hit with a RIFLE round would do the same job as over-kill with a volley of 223) is a blast.
I DO think a lot of people talking about the power of the 223 are talking about a few different guns.
The heavy wounding/keyholing bullet gets largely sacrificed when going to heavier bullets/higher rate of twist that improve accuracy and tactical penetration.
The ultra-accurate 1000 yard AR15s? Yeah, using heavy bullets that don't fit in the magazine.
The 308 is less dependent on bullet type (assuming you stay within the bullet weight/pressure range for mil-pattern rifles) to do damage and punch through things. Noone ever had to make excuses for the 308 that hits its target.
The AR10? Admittedly I've never tried one. As a "combat" weapon you would want a bunch of mags - and they are expensive and a hassle to get. I would also have to question the reliability of mags modified for one gun from another. I've seen posts of the AR10 jamming with mil. ammo; granted this ammo is all over the place in quality but what you may be able to get in the future may vary in tolerances.
If you DO get an AR10 you'll have to get a postban (excluding old stoner guns that are smiliar) - muzzle flash can suck at night, and render a load that you otherwise like too bright at dusk. Try to get one without a brake if possible, or find a way to "block off" the brake - a "combat" gun needs to be able to be fired without earplugs without deafening the guy next to you.
Battler.