The Paladin :
if you have a HD5850 then a GTX960 will be compatible with your motherboard,
you bigger issue with the GTX960 is will your power supply be able to handle its consumption
what make/model is your power supply?
Sorry I forgot to mention that my PSU is a 750 W. ( FSP750-80APG) Model: FSP750-80APG; input rated 100-240V~, 10-5A, 50-60Hz; Output rated (DC) +3.3V/30A, +5V/30A, +12V1/18A, +12V2/18A, +12V3/18A, +12V4/18A, +5Vsb/3.5A, -12V/0.5A, (+3.3V & +5V = 170W max.) (+12V1 & 12V2 & +12V3 & +12V4 =648W max.), Total output power : 750W.