That's a rather unique problem to have. I'm glad you managed to find the problem and easily fix it.
As for the need for a new GPU, that is up to you and the games you play. 8GB can be a hindrance in some cases that will only increase with time. But at least you're no longer in a hurry to buy a new one, so you can wait until all of them launch, see how they compare and what do they offer, and then make a decision.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.