I said I was going to do this and I just got around to running iBench. XBench, which I already reported, tests the overall system performance while iBench zeros in on specific aspects of the CPU itself. And the results are:

32 Bit Mode Composite Score: 4.31
64 bit Mode Composite Score: 4.28

So the Core 2 Duo processor is in fact very slightly slower running in 64 bit mode than it is in 32 bit mode. On the other hand, as I mentioned earlier the overall system performance is better in 64 bit mode and I find the overall "feel" to be a noticeably "snappier" in 64 bit mode, so that is my default mode.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein