The benefits of the Phenom probably come from it's higher IPC count. DOn't get me wrong, I love my 9500. But I think it's a CPU better suited for a desktop computer than an HTPC. Remember that Phenom's are 95W TDP, although each core now has separate voltage and speed control, as well as NB speed control.
And no, the a64 x2s can't benefit from the higher HT bus. AMD will release Phenoms with defective dies as triple and dual cores eventually, and those will be able to benefit from the new 780/790 chipset features. The revised Stepping of Phenoms is due this spring, minus the TLB error.