I bought a flashed AMD 7950 from Mac Vid Cards in December 2015 – I received this (from LA to UK) in Jan 2016 – soon after I discovered it was faulty with glitches, kernal panics and random restarts. I received a full refund from MVC but this didnt include my expenses in shipping the item back (around £20) and I also wasnt refunded the £9 customs ‘admin’ fee – though I got the customs charge refunded (cant remember how much this was).
So overall, I was unlucky by receiving a dud – perhaps something went pop in transit as it did travel a very long distance.
Soon after sending back I decided to buy a bare PC card from Amazon uk because you can send it back if faulty and not loose any money. As of writing, ive been using the AMD R9 380 in my 2010 5,1 MacPro for 25 months and its been great – slightly quieter than the 7950 and about the same power in FCPX (when the 7950 worked that is).
The R9 380 has now been discontinued but you could probably pick one up second hand or try a 280 or a Vega type card – check out macrumors.com Mac Pro forum section for further details
AMD R9 380 Unboxing
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