Went to Newegg to buy, but found there are 8 different model numbers, all for the Sapphire Radeon HD 5770 1 GB DDR5 PCIE. Is there a difference? Also, is there a 'real' difference between the 5770 and the 5740? I ask because I inadvertently orderedd the 5740 and am wondering if the 5770 is worth $40 more? System CPU is AMD Athlon II X4 620. Monitor 20 to 24" (not sure yet).