64-bit leap?

Welp.. Got a new 6800 Ultra in the system. Beautiful card, runs faster, but I'm damn sure I got a pretty bad bottleneck with my 3200+. Why? Because although 90% of the time it's 2x faster than my old 5900 Ultra, there are still places in games (Doom3 and Half-Life2) that run at 30fps. Technically, that's not all that bad, but what bugs me is it runs at 30fps REGARDLESS of the quality settings. I don't have vsync on. It runs the same speed at 640x480 lowest settings in Doom 3 in a certain area as it does at 1024x768 4xAA 8xAF, which tells me my system is choking. The question is: would I see much of an improvement if I upgraded to a 64-bit 3200+ on a dual channel motherboard (I have 2x512 sticks)? I know the processor is no different in raw megahertz, but with a dual channel setup and and direct path to the processor instead of an FSB could I expect much improvement? I'm kinda hesitant to shell out $300+ if it's not going to make a difference. Opinions?

>>6
Modern x86 CPUs (I think as far back as the PII or PIII, maybe even further) already contain more registers internally than are exposed via the instruction set.  Look up "register renaming".  As far as I know, putting the AMD64 into long mode just exposes some of the registers that in 32-bit mode are used for renaming.