New Rig for Quad Boxing - Advice?

[Akoko]

I've been quadboxing on a laptop this whole time and I'm extremely worried that it's going to explode. So I'm trying to build a desktop with NCIX with a budget around $1,800 Canadian. For memory, motherboard and CPU I have absolutely no idea what to pick (hardware newbie here). I've read so many reviews but they all seem to be saying opposite things, not to mention those reviews aren't necessarily relevant to multiboxers.

Anyone have any suggestions? This is what I've picked out so far, although I'm completely open to changing any of these items. I prefer to use only one or possibly two monitors.

Graphics card - from what I've heard it's not worth going GeForce because they are too expensive for almost the same thing and get really overheated.
XFX Radeon HD 5870 HD587XZNFV 1GB GDDR5 2XDVI HDMI DP DIRECTX11 PCI-E

Monitor
LG W2343T-PF 23IN 1920X1080 1080P Black LCD 5ms 30000:1 DVI VGA

Keyboard
Logitech G11 Gaming Keyboard Black Silver Programmable Backlit Keys USB

Case
Fractal Design Define R2 Black ATX Mid Tower Silent Computer Case 2X5.25 8X3.5INT No PS Front USB

OS
Windows 7 64-bit

CPU
My friend said that if you get an ATI card you should get an AMD processor since apparently they make drivers to complement each other. However, AMD seems to be getting killed on all the reviews, especially their AMD Phenom II X6 1090T and 1050T models. Is there any disadvantage to going Intel? How would you think the i7 860 Quad Core Processor Lynnfield LGA1156 2.8GHZ Hyperthreading would perform for multiboxing?

Memory
I'm fairly certain I'll need 6 gigs of RAM. DDR3, probably. But how the heck do I choose between all these options? Isn't the gain from having 'faster' RAM negligible?

Motherboard
I am just absolutely clueless on where to start for choosing a motherboard. If I'm only using one graphics card, should I stay away from anything with the word 'Crossfire' in it? Would I conceivably need to use two graphics cards just to quad box on one or two monitors? The only other games I play are stuff like Mass Effect 2, L4D2, TF2, BlazBlue, etc. so nothing like Crysis.

Anyway, sorry if that was a lot of text for you to read, but I would truly appreciate any help. Everyone is telling me different things and I think my head is going to explode faster than my current laptop. I'd especially appreciate it if anyone could tell me if any particular part I chose is 'limiting' another one's performance, if you know what I mean, thus making it worth choosing a cheaper model.

EDIT: See my post further down for updated specs.