Graphics card core, and clock dilemma

Give the specs of the Dell C521 cos this is becoming a pain to go and check specs ourselves every time.
The cards you have given are both PCIe 2.0 & 2.1, you mobo has a PCI Express X16 Slot. Since it's a dell machine, check for compatibility issues.
If they are compatible which is mostly the case with other mobos, you can go for the Fermi. Although it's going to be performing at lower bandwidths, it will be the better choice for your rig if you plan on playing Physx enabled games.

I would say the 6570 performs better.

AMD Athlon 64 X2 Dual-Core processor

4GB RAM

nVidia integrated video (DirectX 9.0c Shader Model 3.0 Graphics Processing Unit)

PCI Express 1.0A

280 W



website link if i'm just spewing useless info

It may perform a tad better but the bottle neck is going to be bigger, plus it's a 2.1 PCIe where as the Fermi is a 2.0 Closer to his x16 although 2.0 and 2.1 ain't that different but backwards compatibility becomes more and more difficult as you increase the gen gap.

so is this going to be a Plug, install and go thing? or am I going to have to tweak things?

It's going to be a plug, install and go thing.
Tweaking would only need to be done if you experience problems from the Older systems side. The card's not got a need to be tweaked.

well next is going to be me, tracking down that elusive AMD Athlon AM2 6000+ Brisbane...

Do you mean you're going to be upgrading the processor too?

of course!, im Crazy enough to try ANYTHING XD

Good luck to you, keep the Dino alive, and you know what's going to happen in the end.

It's going to eat you.

as is expected ^^

thank you for all of the help BTW  

What did you end up doing and how does it work?

I'm also currently investigating this, and many searches later I haven't found much definitive.

I can add a little info: the +12V is 16A:
http://i52.tinypic.com/m7s19i.png

Dell says that the x16 slot can support 25W max, which I think is the ultimate arbiter, though finding max draw for cards is not easy.
http://support.dell.com/support/edocs/systems/dimc521/e...

Another thread here said that the 8400S would work, though with those you'll commonly see "Minimum of a 350 Watt power supply. (Minimum recommended power supply with +12 Volt current rating of 18 Amps.)"
http://www.evga.com/products/moreinfo.asp?pn=01G-P3-130...

Interestingly, the much higher-end Galaxy GeForce 9600 GT LP definitely works, since I've seen multiple posts to that effect, but who's actually selling it now? It seems to be quasi-discontinued despite no mention on the vendor's site. Also, confusingly, the vendor site it needs 300W with 12V @ 26A, so you would think it would have no shot on the C521, yet people say it does.
http://www.galaxytechus.com/usa/productview.aspx?id=79

I ended going with the ATI Radeon HD6570, it works fine. HOWEVER i did have to cut a small VGA shaped Hole in t he side of the case for it to work with the side on. like i said it works just fine, but unless you can only use VGA and dont have a Dremmel Tool you will have to leave the side off of the C521.