I finally got around to running a benchmark comparison between running 64 bit mode and 32 bit mode on my 24" iMac 3.06 GHz core 2 duo with 4 GB of matched RAM. The results follow with 32 bit mode first and 64 bit second. The "winner" in each category is highlighted in red. Note this is the result of very limited trials and I do not pretend it to be scientifically valid. It is merely a data point.

System Info
Xbench Version 1.3
System Version 10.6.1 (10B504)
Physical RAM 4096 MB
Model iMac8,1
Drive Type WDC WD5000AAKS-40YGA1

32 Bit Tests
Results 157.13
CPU Test 218.71
Thread Test 369.12
Memory Test 222.32
Quartz Graphics Test 239.47
OpenGL Graphics Test 101.17
User Interface Test 307.02
Disk Test 64.71

64 Bit Tests
Results 165.75
CPU Test 184.85
Thread Test 406.08
Memory Test 224.22
Quartz Graphics Test 244.88
OpenGL Graphics Test 102.42
User Interface Test 329.76
Disk Test 76.81

Surprises:
  • The 32 bit CPU score being 18% higher (faster) than the 64 bit score
  • The 64 bit Disk Test being 18% higher (faster) than the 32 bit score
  • Although the 64 bit overall score is only 5% better than the 32 bit score, 64 bit mode "feels" a lot snappier. I can only attribute that to the impact of the greatly improved disk performance in the 64 bit mode.
The next thing to try is iBench to see if the 64 bit/32bit differential shows up there.

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

— Albert Einstein