I mean, my 6870 sounds like a jet engine on medium, so, ya know, they need to lower the quality of the graphics a bit IMO.

manually lower the fan speed. my 6770 fan is at 70%-ish on medium with light bleeding and gameplay DoF and i get 72 celcius max

How do you do that?

Or buy a customized cooler that both cools your GPU better and more silently. You'll have to research what type you need though.

And also limit your FPS, too high FPS can make the GPU go nuts. Either just run with VSync or find a FPS limiter.

MSI AfterBurner can give you control of your fan, overclock/underclock, limit FPS and give you information about GPU in-game as OSD, don't know how good it is with an AMD card.

As for Witcher 3 requirement, expect it to be relatively more demanding than Witcher 2 considering it's going to be open world but if they optimize it and let you control view distance I don't think it will that much worse than Witcher 2, still a reliatvely modern med-end card will be preferable (my guess).