Two 290X is obviously going to be better than the 980 in crossfire enabled games but if you're talking single, then I would say it depends on the resolution. I believe in 1080p you're looking at a marginal difference of 10-15%, which is also explained by the price. At QHD the gap probably narrowed to 7.5-10% and 2.5-5% on 4K. What I like from Maxwell however is the Power consumption/Efficiency, as it is really really good.