CPU confusion

Hi there,

My current system spec is as follows:

Athlon 64 x2 4200+
EVGA superclocked 8800GT
2 Gig DDR 2 800
500w PSU

I mostly use if for gaming and so the upgrade will be for this.

Now, I have been looking into what CPU to get but it all seems confusing. I think I am right in saying that Intel have the upperhand in performance at the moment and so I have been looking at the Intel chips.

What I don’t understand is the numbering system Intel are using, if possible can anyone post a link to something that explains this. i.e. what is the difference between the Q9300 and E8200. After reading the forums the Q6600 seems popular, is this just because of its overclocking potential?

If you guys had say $400/£200 to spend on a CPU for a gaming rig which one would you choose?

Bearing in mind my current CPU is an Athlon 64 x2 4200+ how would you rate the CPU you choose over this? The reason I ask this is I am wondering how much of an upgrade the highest end Athlon dual core would be 6200+ I think?...

Obviously I have to choose between dual and quad core and from reading the boards it looks like dual core is best for gaming at the moment - although if I did go for a quad core, would games optimised for dual core be able to use 2 of the cores on a quad core?

This is really confusing for me so any informative information would be a great help as I don’t want to regret buying the wrong CPU.

Also, could you recommend a chipset to go with the CPU you recommend.

Oh an one last thing - I haven't researched this yet but I will probably get a new grapics card as well so I was thinking of buying another 8800GT and putting them in SLI. Would this be a good idea or would getting 4850 be a better idea?.

Thanks for reading