thanks.
So the mini-30 is better for closser stopping power, which would be good for a "city" environment.
If you're going to go 7.62x39, you can get a SKS or an AK clone for less money. The MSRP for a mini-30 is $809, you can get a Yugoslavian SKS for $179, or a Hungarian or Romanian AK for around $4-500. I'm not an AK guy, so look around for better info.
Personally, in a city environment, I'd choose a 12 gauge pump shotgun. Less worry about over-penetration.
In fact, I just picked up some Winchester "Super Speed Xtra" shot shells. More muzzle velocity (IIRC 55 fps) than their standard shot shells, and "hard shot for improved patterns" and "improved knockdown power".
With that being said, if I had only the .223 and 7.62x39 to choose from, I'd buy something chambered for the 7.62x39, and load it with soft-point hunting ammo. (Or 7.62x39 hollow-points.)
But I don't live in the city.