Dynasty said:
No. Comparing brass to brass and steel to steel, factory 7.62x39 is cheaper than .223.
However, reloadable .223 brass is cheaper than x39. Both take around 25gr of powder (give or take, depending on powder and bullet), and use different size primers. Much more variety of .224 bullets versus .310-.311 bullets.
.223 AK mags are also more expensive than x39 mags. More and cheaper x39 parts available too (brakes, bolts, barrels, etc.).
Dynasty said:
Less stopping power? Yes.
Very debatable. A heavier bullet doesn't mean it has more "stopping power." Bullet wounds from true M193 ammo are very nasty. Expansion of current Russian soft point ammo is sketchy and Russian ammo as a whole is not nearly as accurate (platform not withstanding). There's a bit less recoil in .223 compared to x39 as well so you also get quicker follow up shots.
Dynasty said:
Even though I have a 12 ga for HD and SKS in 7.62x39 for longer ranges I do not plan on using the AK for HD
This thread debunks most shotgun-for-HD myths:
http://www.ar15.com/forums/topic.html?b=3&f=118&t=368751. They concentrate on the AR, but many defense rifles meet the criteria.
Dynasty said:
for a bigger plinker than the .22LR is the .223 AK a good choice?
Plinking with ammo that runs $200-$400+ per case is not the best choice. You'd be better off buying a 10/22 instead.
I have a .223 AR and an x39 AK. Both are nice rifles. The AR is more refined and more accurate. I have considered a .223 AK solely because I reload for both guns and it's easier to have fewer types components and tools on hand.