That seems acceptable.
I'd say yes, at least if it fails, you can get new one for free. RAM is rather cheap though, so you could just buy new one if it fails too. If you're going to overclock then you have to choose the corsair but if not you can just go with the cheaper and if it starts BSODing in the future because of RAM failure just buy new, preferences really.
Actually I lied before, I have a 6950 not 6850 so not sure if you'd be able to run things like you want in the future but the next step up is a lot more money so probably not worth it.