Will ignore Graham's quite frankly stupid remark and try to give a reasoned answer
To start £100 not going to give you a gaming card if you can push to the £150 -£160 region you should be able to pick up something around the Gtx 480 mark wich will give you reasonable low to mid range performance depending on game
£280 will buy you a Gtx 770 which will give you mid range to high end performance depending on game if you want out and out high end you looking £40 plus for a card
but would seriously look above £100 for a decent games card as it wont happen
Devil Fish , found your reply hard to read (old fashioned no doubt). Had to read it a few times to make sense. Then again I don't use a smartphone to reply often and usually not a tablet either. Both mostly text freaky language for the lazy.