The two video cards named come with 1gb of GDDR5 ram. However that is pretty much an irrelevant spec as it would be the output of the GPU over the RAM quantities. It's feasible to have lower quantities of RAM and higher clock speeds with no bottlenecks and achieve the same goals. So giving the required specification of card in a manufactures lineup is a far better way to give requirements.
But I suppose you could ask is the 6790 any good for example as it's an older model but in a higher range.