The goal is for the two cards to compete directly with the X600 series, offering many features found with the GeForce 6800 models as well as new features such as native PCI Express support.
While the GeForce 6600 may or may not compete with the X600 on a performance level, it is the most economical version available from either company. With a low $149 MSRP, the GeForce 6600 looks to be in a class by itself, offering native PCI Express capabilities on the cheap, with 8 pixel pipelines.
The GeForce 6600 GT, on the other hand, has the makings for a solid contender for the X600. With 8 Pixel Pipelines and faster GDDR3, the GeForce 6600 GT is poised to steal the show. While offering native PCI Express, GDDR3 and SLI support, the X600 appears to be out gunned every step of the way when compared to the GT. We don't know of 256MB models down the road, but ATI's 256MBs of DDR memory may not be enough when you weight the options between the two lines. But there is still time. The down side is, both new NVIDIA models initially will only be offered in PCI Express flavors and it may take a while longer for AGP versions to hit retail channels.
NVIDIA has been careful to pick their battles with ATI, offering a cheaper, lightweight alternative to the X600 line with the GeForce 6600 and a direct competitor to the X600 in the 6600 GT. The GeForce 6600 GT looks to be better equipped all around while competing with the X600 dollar for dollar. Not only are we intersted to see how these cards perform on the test bench, we are equally curious to see how ATI responds to NVIDIA's latest offerings.
As far as availability goes, don't expect to see these models on retail shelves much before October, but e-tailers and OEMs should start offering them as early as September.