Computer upgrade for BF3 - Advice needed

Here is my current build

Asus ROG Maximus III Gene 1156
I5-750 stock cooler
XFX XXX 5850
Seasonic X-650 PSU
8GB CL7 RIPJAWS 1600 MHZ
120 Go OCX Vertex 2
500 Go 7200 rpm HDD
ANTEC mini P180 case
Dell UltraSharp 21 inches 1680x1050 resolution ( Also considering using my 40'' 1080P HDTV )

I might be ready to invest a few hundred dollars to keep my gaming computer "up to date". I've suffered so much during college / university playing on a normal laptop that I want some eye candy!

Also, my wife is a amateur photograph and she does a lot of Adobe Lightroom on that computer. So if an upgrade is good for her, all the better.

Finally, I like my computer to be fairly quiet since it's in the kitchen/living room area.

Budget would be in the 300-400$, but I don't mind NOT buying that much and keeping my money for other hobbies.

So I've got a few ideas and looked on some sites, but I cannot decide.

1) Keep all my money for a GTX570+ / 6950+ (300-400$ or so)

2) Upgrade motherboard/cpu to I5-2500k or better and keep my 5850

3) Buy a Noctua D14 and OC my cpu for 100$, keep 200-300$ for GPU

4) Find a used 5850/5870 on Ebay and crossfire ? I'm unsure about the scaling with the 58xx.


Thanks for all your advices!