I don't even know where I am in this post. But, there is no doubt that faster processors will speed up your computer and will allow your computer to process the demands and therefore the queries. Moving to 12GB of RAM doesn't seem like it would have that much of a difference. It would have given you 11GB of free RAM rather than 3GB, so XP would have run faster. Still wouldn't have allowed SQL to work faster as far as how it stores and delivers data. It WOULD all SQL itself to work faster IF the 4GB had not been enough.
The cutoff for me has always been 5GB, which most people don't use. Generally, with 6GB of RAM you won't find yourself rebooting your server once a week. Of course this must have been 64-bit.
