Have several HTPC's in use here.
All were mobiles running around 2100MHz, in NF2 with MCP-T (Soundstorm).
Have now upgraded most to Opty 144 and 146's, overclocked to 2700MHz or 3000MHz.
Not at all impressed with A64 performance compared to XP-M.
For gamers, CPU means little.
Going from a 2GHz XP-M to a 3GHz A64, may give you a 10% gaming performance boost.
Video card is what makes the difference.
Going from a $50 video card to a $100 video card can give you a 300% performance boost in games.
HDTV is why I made the move, and again, not trilled at all with the small gain in performance. Maybe 5% faster with Opteron.
Plus, going to Opteron means I had to give up good audio. Sure, HDA is O.K., but you still can not game over S/PDIF like you can with Soundstorm.
The real advantage to upgrading is video card choices.
Socket A is limited to AGP, while I can now run PCIe.
Still, high end AGP cards do perform great with most of todays games.
If I had to spend my own money, (I sell what I have after testing, so it's not my money really), I would keep XP-M, and wait until the next wave of motherboards and CPU's, hoping that they would finally give that WOW and smile after upgrading.