I just bought a non-reference ASUS 7970 DirectCU II card (non-factory overclocked) for under $400 and I felt it was a decent mining catch until I started looking at more reviews...

Apparently, these cards are very difficult to overclock at all with the voltage factory locked. I'm a layman when it comes to mining (I fire up Sapphire Trixx and go), so I'm wondering if anyone has an enlightened opinion on whether the DirectCU II is worth it for mining or whether the TOP version (factory overclocked) would be better? Perhaps these cards are simply not the best 7970s for mining?

Thanks.