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I'm seriously considering upgrading from my current HIS Radeon HD 5850 iCooler V Turbo 1024MB to one of these at the end of the month.
Might be a strange question, but will I notice a huge difference?
but i dont think there has been a single case of the toxic not unlocking to 6970
Well, the straight forward answer would be "no", not 'huge' gains. However, you should notice better minimum and average frames per second so it should feel even smoother, though I expect your current card delivers smooth frame rates anyway. Heres a rough guide in performance difference, just be aware that drivers will have changed a lot since then. Personally I'd hang on for the 7000 series, unless you really don't want to wait and your 5850 isn't performing as well as expected.
http://www.anandtech.com/bench/Product/293?vs=295