I bought a Q6600 quad processor with Windows XP Pro 64, principally to handle a calculation that takes 50 hours on my other system (Intel T7200 2GHz Core 2 Duo). The software concerfned makes use of multiple processors.
The following highlights are reported here:
I would have expected the 2.4GHz Quad system to deliver a result in around 21 hours (given the relative power). It took 23 hours and I put the difference down to background taks such as anti-virus.
I use Adobe Acrobat quite a lot to render output from a number of sources. It has to be Acrobat 8.x with XP 64 bit. Don't even bother with Acrobat 7.x.
If you're wondering about Internet Explorer 32 bit versus 64 bit - here's the skinny that I have found matters. JAVA. I couldn't find a 64 bit Jave Run Time Environment.
Fortunately, the 32 bit browser works perfectly well in XP 64 Nand with it, JRE 32 bit.
The quad processor is good for only two things (otheriwise nothing runs faster that on any other system of same CPU speed):
1. Multi-threaded applications that can use all available processor power;
2. Your own multi-tasking; such as a DVD burn whilst browsing, or downloading or word processing.
I couldn't see any gain for the 1333 FSB capability of the motherboard over the 667 that I have on the T7200 system. I dare say that might be different on memory and disk intensive applications - but on CPU intensive work, there appears to be no gain from the fast memory.
When installing software, XP 64 places 64 bit applications into Program Files and 32 bit applications int Program Files-x86.
Windows XP 64 SP2 works well enough and I'll add to this post as I see other applicatins perform, particularly from the Adobe stable.