My system - it's been a while...

[Ever]

TLDR:
I'm curious what's changed since I built this computer, and how much I should spend on my next computer that will run max-setting Diablo 3. My standards are much different than yours, so I'd value a more experienced and global opinion, rather than that of someone who might over-nitpick the details. (IE, "dood you gotta get the new Over-9000GTXXX," versus, "dude, you used to have a freaking 8600GT. Just buy the 6870 and you'll run max settings at 60fps with a room full of spells being cast and skeletons exploding.")


Longer:
I like to research things and knowing that I made a sound purchase. That said, I'm about to upgrade for D3, and I'm older now. I don't have the time or energy to put towards countless hours researching what in reality are minute differences between similar CPU's and GPU's. I'd simply like to buy a computer that will run it at max settings, in multiplayer with a lot of simultaneous on-screen action, and on a great monitor. That's about it.

I don't doubt this has been asked before me. I guess the reason I'm making my own post is because I'm wondering if I need to upgrade monitors. If I need to get 2560x1400. And what will be required to do this without hiccuping in multiplayer like it did during the beta. Thus, please take a peek at my current computer below and let me know what I should upgrade to go from this to "max settings" in D3, monitor included. Any fast-track update on what's happened between this generation of build to now gets bonus-points!

Lastly, what kind of bonus am I going to see between upgrading my computer and monitor (~27in, 2560x1400), and just upgrading my computer and keeping this monitor (24in 1920x1200)? I think this will be one of the major factors in whether I go budget or go big.


Intel Core2Duo E6400 2.13ghz (OC'd to 3.12ghz)
Nvidia GeForce 8600GT 256mb
2gig DDR2
Monitor: Dell 2405FPW (max res 1920x1200 16:9)
See sig for details

1) What will you be doing with this PC? Gaming? Diablo 3 and web browsing
2) What's your budget? Not sure. <$1k. But my post isn't about what to buy, rather trying to start a convo on upgrade options.
3) Which country do you live in? USA
4) What exact parts do you need for that budget? CPU, GPU, RAM, PSU, MOBO, case
5) If reusing any parts, what parts will you be reusing? 1TB 7200 HDD
6) Will you be overclocking? Perhaps
7) What is the max resolution of your monitor? 2405FPW 1920x1200
8) When do you plan on building/buying the PC? 1 month
9) What features do you need in a motherboard? I enjoy having up-to-date Ins/Outs for peripherals
10) Do you already have a legit and reusable/transferable OS key/license? 32bit Win7