Sapphire HD 6670 DDR3-1600 2GB should be a good choice. HIS IceQ H657QO1G
(HD 6570 DDR3-1600 1GB) is another choice, but the price difference after rebate is very small.
The only difference between HD 6570 and HD 6670 is the core clock: 650MHz vs 800MHz. Memory varies with the model. HD 6670 often comes with GDDR5 (4000MHz effective frequency) and such a model is pricier. For video playback, DDR3-1600 1GB is enough.
BTW memory bandwidth is calculated this way:
- memory bandwidth = (memory bus width) x (effective frequency)
HD 6570 / 6670 has 480 Radeon cores and 128bit memory bus, so
- With DDR3-1600, memory bandwidth = (128bit) x (1600MHz) = 204800 Mb/s = 25600 MB/s = 25.6 GB/s
- With GDDR5-4000, memory bandwidth = (128bit) x (4000MHz) = 512000 Mb/s = 64000 MB/s = 64.0 GB/s
HD 6450 has 160 Radeon cores and 64bit memory bus. So the memory bandwidth is halved. But for BR 2D/3D playback, you won't see any difference. If you add more video post processors (deinterlacing, denoise, sharpening etc.), there are differences and 6670 > 6570 > 6450 (">" = "is better than").