There will be two versions. One with GDDR2 memory at 900MHz and one with GDDR3 at 1600MHz. Both have 128-bit memory interfaces. A review posted at Chinese site zol.com.cn and reveals performance which is just slightly better than GeForce 8600GT, which isn't all that surprising since the product specs are really similar.
Just like the rest of the series 9 products, this product isn't all about performance, but PCIe 2.0, lower power consumption and an updated PureVideo HD.