What people don't realise is that when a 64-bit processor is running 64-bit software anyway it will fell as slow as a 32-bit processor running 32-bit software, because the 64-bit software is that much more complex !!!!!
It won't be any faster at all. The only reason why Athlon 64's feel faster is because of the hypertransport, integrated memory controller (no FSB) and increased clock speed and cache.
When Athlon 64 CPUs are running 64-bit software they will actually feel as slow as or slower than a modern day computer running 32-bit software, because the CPU will be used up more, or more "fulfilled" you could say, because it is being used to its full potential, so it will seem slower. When a 64-bit CPU is runing 32-bit software it will seem very fast. Not so in 64-bit.
Just like the 286 and 386 processors. The 286 was 16-bit could only run DOS but when the 386 came out it enabled 32-bit and therefore "multimedia" as we know it today. But it still felt "slow" to use. 64-bit does NOT mean faster, just more flexible.