AMD's Radeon HD 7000-series onslaught continues, with still no 28nm retort from NVIDIA. The latest offerings are the 7870 priced at $349, and the 7850 priced at $249. Both are based on the Pitcairn GPU and hog the mainstream gamer spot below the Tahiti-based 79xx cards and far above the 77xx options. In terms of competition, these cards go head-to-head with the older NVIDIA GeForce