R.I.P HD 4870 *Edit*

What kind of powersupply do you have? It depends a lot on if you have to buy just a GPU or a GPU + PSU.

ati 7870 or 660 gtx

but what is the rest of the pc.. psu, cpu, monitor

If you want to spend ALL those 400€ you could go for an HD7970 GHz Edition or a GTX770. Here's a little comparison of the two. You can use that page to make your own mind and check other cards as well (some may be under the "GPU 2012" section).
Also make sure your CPU won't bottleneck your new GPU! :)

It's hard to tell without knowing anything else about your computer. Buying a GPU worth 400 Euros would be a waste of money if the rest of your computer bottlenecked it. And if it's the same computer you bought with the 4870 years ago then you will have a bottleneck for sure.

680 Nvidia sounds like it would be your best option GL

i own an hd 4850 and 4890 both are unning in good condition
please explain how it died?
artifacts or just black screen?
did it overheat before death ?

7850 or 7870 should fit your computer just fine.

In case you are green, then 660. Later this year 7xx generation is to come, so if you are in no rush, you might want to wait. The announced 770 looks decent, but is definitely an overkill compared to the rest of your PC.

ViewSonic 1440x900 19:10::
This is his resolution. Getting some powerful card is wasteful for a monitor that small.

A 550ti or 560ti would work really well at your resolution. Getting a new everything would be a big help considering your absurd system specs. A 850 watt PSU for one card? 16GB RAM...

Maybe you should see a system building thread. Wait a few weeks and you can get a Haswell CPU.

I just purchased GTX 780 so I wouldnt know how good that card performs compared to my aging 480.
GTX 770 looks really good and Radeon 7970 is similar to 770 in many aspects including price but 770 is newer.
Im nVidia fanboy so my reasoning is very biased.

the best graphics card you can buy without the AMD Phenom II x4 3.4 GHz limiting performance in games is the AMD Radeon HD 7790.

if buying a larger monitor such as 1920 x 1200 the best GPU you can buy without running into a CPU bottleneck would be a nVIDIA GeForce GTX 660

i suggest u change ur cpu and mobo otherwise any high end card will bottleneck