My favorite take on 64 v. 32 bit is:
http://www.statacorp.com/statalist/archive/2005-07/msg00828.html

On 3/5/07, John Fultz <[EMAIL PROTECTED]> wrote:
> On Mon, 05 Mar 2007 08:14:22 -0500, G. Vincent Castellano wrote:
> > I was helping someone get set up with 0.95 and noticed that the machine
<snip>was an Athlon 64.

<snip>  the performance advantages of 64-bit are dubious.  If you do a Google
> search on this, you'll find all kinds of comparisons which show that, for
> similar 32 and 64-bit applications running under a 64-bit OS, sometimes the
> 64-bit outperforms the 32-bit, but sometimes the 32-bit outperforms the 
> 64-bit.
> 64-bit is not theoretically faster, and that's not its principle advantage.
> I've not done a large amount of research here, but I think the main 
> differences
> can probably be chalked up to...
>
> 64-bit speed advantages
> + Larger registers
> + 64-bit OS doesn't have to do 32-bit address translation
> + Possible on-chip optimizations
>
> 32-bit speed advantage
> + Since pointers are 32-bits, apps use less memory, causing fewer cache misses
> + Better evolved 32-bit compiler optimizers because the technology has been
> around longer
>
> The real advantage of 64-bit isn't speed, it's memory.  Since Quackle remains
> well within 2 gigabytes of usage, that aspect of the 64-bit advantage simply
> isn't an issue.

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