I'll actually go against the trend here and say that even in multithreaded titles I'm skeptical as to whether the PD-820 can overhaul the A64 3800+.
Going by the following Oblivion CPU scaling charts
, a PD-820 would only score around 29fps (they don't list it in the charts, but the 2.66GHz PD-805 scores 27.4fps, and the PD-820 would only be slightly faster) whereas the 3800+ is scoring 37.6.http://anandtech.com/cpuchipsets/showdoc.aspx?i=2747&p=3
It would take a very
heavily multithreaded game for a PD-820 to overtake a 3800+.
I suggest if these are your only choices, and you don't intend to multitask much, to get the A64 3800+.