An 8150 and 6212 are both BD based CPUs. Server CPUs are clocked lower for reliability reasons, and Opterons are no exception. Expect to pay more for less performance.
There are three main differences you'll see between the two.
1) Physical Package: The 8150 is Socket AM3+ and the 6212 is Socket G34
2) MCM: All socket G34 CPUs are built from two dies, so the Opteron is really comprised of two quad cores instead of a single 8 core. This means you get twice of everything else on the chip: quad channel memory, twice the cache, etc.
3) Frequency: Desktop chips tend to be clocked higher for a given price point. This is true of the 8150 vs 6212 as well.
Both can use ECC memory, though many desktop boards don't expose the option in the BIOS anymore. I don't think desktop boards ever support registered memory, however, unlike the server platform.
You mentioned both a 6212 and 6272. My comments are with regard to the 6212 since it is an 8C part. The 6272 is a 16C (dual 8C dies).