GIGABYTE 1024M GTX560 N560OC-1GI DDR 5 PCI-E or SAPPHIRE 2048M HD6950 FLEX DDR 5 PCI-E?

Hello! Need some help here so at 1st i wanted to buy GIGABYTE 1024M GTX560 N560OC-1GI DDR 5 PCI-E but it turned out that i have a bit more money and now i can buy SAPPHIRE 2048M HD6950 FLEX DDR 5 PCI-E and i cant decide which should i buy and i am a bit confused the ati has OpengGL 3.1 - 3.2 but the Nvidia has OpenGL 4.1 can someone explain the difference should i buy the cheaper Nvidia or the Ati with more memory and what about the temperature of the cards which one is cooler?