Well, for one, aospCMod gets updated frequently. They both use Zefie's kernel, as far as I was told. They both now run 2.3.3.
But from experience, battery life lasted longer on Zefie's. Idk why as they are both synced with CM source. But Zefie's had just a little tiny more drain compared to 2.2 roms (Rodimus, RedRevolution). With aospCMod I lose about 5% every 30 mins just on idle screen off.
However, others using aospCMod said they had good battery life, average, but a lot better than mine, nonetheless. So my reports are only my experience. I may have something running in aospCMod that I overlooked (though I have the same exact setup between the two 2.3 roms).
I ended up jumping back to RodimusRom because I couldn't stand the battery life. And I wanted aospCMod over Zefie's. But if you want to use a 2.3 rom, definitely go with aospCMod. It's more updated (frequently) to resolve bugs and other issues, despite MY poor battery life with it.
I noticed aospCMod has better graphics, it's a little bit faster for me. Zefie's CM7 has better changelog updates. The launcher is different in aospCMod, I changed it to GO Launcher EX because it performs better.
Yes they both use the latest Xionia kernel by zefie.