I would go with the cheapest one, the Gigabyte 6850 with the Windforce cooler. It will be much quieter than the MSI Cyclone and just as effective.
I would get the 6850 and overclock it to match the performance of a 6870, rather than buy a 6870. The 6870 has very little overclocking headroom, so an overclocked 6870 won't be much better than stock. The 6850, on the other hand, has plenty of overclocking headroom to match the performance of a 6870.