Ok so i have Msi b75ma e33 Mobo, im looking for some used gpus and i have found Gtx 580 Direct CU 2 for 100$ and HD 6990 power color ( guy gives me 2 months guarantee ) For 95$ which shall i buy? Allso Gtx 580 Is fat card is it going to fit on this mobo? Picture of 6990 https://www.techpowerup.com/gpudb/images/b510.jpg and picture of 580 http://images.bit-tech.net/content_images/2011/02/preview-asus-geforce-gtx-580-directcu-ii/asus-gtx-580-directcuii-3.jpg