Hmm, the board only support AGP card, right?
Then the strongest card you can get is HD3870 AGP version...
Not sure about bottlenecking, but that's the best you can get for AGP board, there's also 4670 AGP, but still 3870 is more powerful...
Oh, so it's the one that support pcie slot, so this is it, even that 8500GT is an overkill for P4 CPU. So, better save your money, stay with 8500GT and BUILD your next gaming PC.