I would suggest a HD7950 for that price point you can find one on Alternate.de for around 300 euro.
zum beispiel : http://www.alternate.de/html/product/GIGABYTE/GV-R795WF3-3GD_WindForce_3X/979690/?event=search
you could also go down the Nvidia root and buy a GTX 660 ti, depending on what games you play it can out perform the AMD HD7950 on some occasions (and you will also save some money as its a little cheaper).
For a little overview on performance here is a decent comparision article - http://www.hardocp.com/article/2012/08/23/galaxy_gtx_660_ti_gc_oc_vs_670_hd_7950/4