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750Ti
Low profile linky please mate
If he has an apu wouldn't he be better off getting a card that's compatible with it for dual graphics?
http://www.cpu-world.com/info/AMD/Recommended_graphics_cards_for_AMD_dual-graphics.html
You could try and source an Afox 7850 low profile, unfortunately most UK e-tailers don't stock them,
http://www.afox-corp.com/en/products_details.asp?proid=209&typeid=46&id=46
What wattage can the PSU provide?
I've shared my steam Libary with him..he tried to run ARK but I had to run 640 x 480 lol
I think he will be happy with 720p tbh... at medium settings..
He downloaded Lost Coast and it ran OK until things got busy when you put the Lamp thingy into the machine.