Hi there

As above I would go with any new GPU or older GPU,really depends,do you plan to render with Octane or Luxrender ?

If do you plan to render too with Octane then I would go with GTX770 which should be OK for yours needs and if you do plan render with LuxRender and Reality then new R9 series are best,like is R9 280 which should be enough for yours needs and still you can play most of the games in 1080 in high settings 

Those cards are now cheaper and you should be able to pick up them for good money there

Hope this helps

Thanks,Jura