560TI is probably your best bet. For £190 you can pick up a Palit GTX 560 TI 448, which is just a tad slower than a 570 which are usually around £220 and above nowadays.
You may want to check Ebay and if you are in the UK Gumtree.com, I have seen a 580 for £180 and a few between £220 and £280 floating around today on forums, Ebay and Gumtree. I know it's over your £200 but if you can stretch a bit more it's worth it.
People are selling off their 580s so they can grab a 680 and bargains are being had
GTX 560TI, GTX 570 or even a second hand GTX 580, would be my choice. There are some great deals around at the moment with the new cards released and people getting rid of their old cards if you are looking 2nd hand I would look into the GTX 580's. However if you are after new I would look around for a GTX 570 or GTX 560ti.