Overhaul my computer! - Need component recommendations...

[Peli]

OK, so I've got a budget of about $800 and I'd like to upgrade my existing computer while reusing as many components as possible and basically build a best-bang-for-my-buck rig (I have the ability to spend more, but I don't want to go too gung-ho). Edit: Actually, for discussion's sake, what would an $800, $1000, or $1200 budget get me?

I 5-box and the lag in places like Org has been getting more and more annoying. I don't ever intend to do more than 5-Box, but I also want a rig that can handle Guild Wars 2 (I doubt I'll multibox GW2) and Diablo 3 without missing a step.

Here are my current system specs (along with what I intend to replace)

-Asus P5N-D Mobo (Replace - no idea what to replace it with)
-Core2Quad Q6600, stock clock (Replace - i5? i7? Sandybridge? Wait for Ivybridge?)
-6 GB DDR2 RAM (Replace - I'd like 16GB or more DDR3)
-EVGA GTX 260 (Replace?)
-1kW PSU with plenty of 12V rails (Bought it to do SLI before I found out that SLI was a waste of money for what I wanted to do - Reuse)
-120 GB Intel 320 SSD (Reuse)
-(2) 1TB Mechanical drives (media storage) (Reuse)
-Standard CD-RW drive (Reuse)
-dedicated 1GB Ethernet card (don't need ethernet ports on my new board - Reuse)
-Thermaltake full size tower case (Reuse)
-Windows 7 Pro 64-bit (Reuse)

Thanks!