Help upgrading GFX, RAM pos PHYX

[yo1dog]

Hello, I need some help upgrading my computer. Here is what I have now:
Mobo: NVIDIA nForce 680i SLI ATX (http://www.nvidia.com/page/nforce_600i_tech_specs.html)
RAM: G.SKILL G.SKILL 4GB(2 x 2GB) 240-Pin DDR2 800 (http://www.newegg.com/product/product.asp?item=N82E16820231122)
GFX: 2 NVIDIA GeForce 7600GT (http://www.nvidia.com/object/7_series_techspecs.html)
CPU: Intel Core 2 Quad Q6700 Kentsfield 2.66GHz (http://www.newegg.com/Product/Product.aspx?Item=N82E16819115027&Tpk=Intel%2bCore%2b2%2bQuad%2bQ6700%2bKentsfield%2 b2.66GHz)

For the new GFX cards I would like to have DirectX 10 support and for under a total of 450$. I'm looking for 4 gigs of the best RAM available that will fit my MOBO and is under 150$ total. I was also wondering if it is worth the money to buy a PhysX processing card. Comments?

I was thinking of getting two NVIDIA GeForce 8800GT (http://www.tigerdirect.com/applications/searchtools/item-details.asp?EdpNo=3509852&body=MAIN#detailspecs) for a new GFX cards and two OCZ SLI-Ready Edition Dual Channel 2GB(2 x 1GB) DDR2 800 (http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3079597&body=MAIN#detailspecs). Comments? Please tell me if both of these are fully compatible because I don't know how to tell for certain. (Not sure about the "SLI-Ready" and "Dual Channel" properties of the ram so if someone could explain that to me I'd be great full.)

For Christmas as kinda an impulse buy I bought myself two NVIDIA 8400s only to find out when I got home that they where not sli compatible... which makes no sense to me considering my older current cards are. But whatever, I can just take it back for a refund.

Thanks for your help,
- Mike

[Northwood]

2 Graphics cards really isn't worth the money for the 30% boost methinks, you'd be better off with the highly acclaimed 8800 GTS 512, the MSI version comes with 730Mhz core clock and isn't much more expensive than the 8800GT, but will surpass 8800 Ultra performance with some tweaking.

As for memory the Crucial Ballistix 8500's are really cheap at the moment and clock like hell, dunno about dollars but in the UK 2 x 2GB kits comes to about £140 (2x1GB per kit so 2 kits = 4 sticks) or even the Ballistix 6400's if they have the micron IC's, will be cheaper and overclock the same.

I wouldn't touch a PhysX card at the moment unless you're a UT3 fanatic, but even then the physics only work for offline play, not alot else thats supporting PhysX, i'd really wait until it takes off before you invest, could be a costly mistake otherwise.