Did you trying changing some of the configuration file settings for msi afterburner? It is locked by default.
Can you explain a bit more about that? I think that's what I'm getting with my 5870, It simply refuses to budge over 900Mhz core, if I set it to anything higher it just drops back to 900Mhz.
I thought there may be a bios lock on it and I've been thinking about flashing the bios to overcome it.
If I can do it with afterburner, I won't bother flashing.