AMD's Radeon HD 6870 and HD 6850 graphics cards are here, but they might not be what you expect -- though alphanumerics suggest they'd succeed the lauded Radeon HD 5870 and 5850, these new "Bart" chips are actually a pair of solid plays for the PC gaming mainstream. $180 buys you a Radeon HD 6850 with 960 stream processors, a 775MHz core clock and 1GB of GDDR5 memory at a 1GHz effective rate, and $240 nets the HD 6870 with 1120 stream processors and 900MHz / 1,050 MHz clocks respectively. On paper that puts them a good bit behind the finest, but a collection of reviews show they can keep up with the pack, as the 6870 consistently m
