Everyone in this thread should read
http://www.FirearmsTactical.com for a background on terminal ballistics,
http://www.ammo-oracle.com for terminal ballistics data for assault rifle cartridges, the 6.8SPC FAQ for general info (see my .signature), and this thread over on THR where we've been discussing it lately:
http://www.thehighroad.org/showthread.php?t=130193
In particular, note that the terminal ballistics for 7.62x39 suck. The bullet doesn't fragment at all.
Also note how different (ie, worse) even the 77gr Mk262 ammo is from the 6.8SPC terminal ballistics.
-z