1920 x 1080 Benchmarks
At 1080p, it's pretty clear Nvidia has the advantage. The robust 512-bit memory configurations of the 290 4GB and 390X 8GB don't really come into play at this resolution. So we see the GTX 970 beating the R9 290 at both reference and overclocked settings, and the R9 390X being quite frankly outclassed by the GTX 980, which is truly an ideal 1080p card.
2560 x 1440 Benchmarks
Keeping in mind that our manually-overclocked Sapphire R9 290 Tri-X performs about as well as a factory-overclocked R9 390, like its successor the Sapphire Radeon R9 390 Nitro (which sports clocks of 1040MHz/6000MHz), there's no doubt that these cards are great mid-range choices for 1440p gaming. They'll outrun the reference GTX 970 pretty much across the board. But once you take into consideration the 970's big overclocking headroom (and typically-large factory overclock), it's a tougher call. Given the GTX 970's less optimal memory configuration (only 3.5GB of its 4GB runs at full speed), it's probably not the best long-term choice for 1440p monitors, so as between the two, we'd probably go with the 290/390.
That being said, an even better choice is the 390X 8GB. Averaged across our three games, it easily matches a fully-overclocked GTX 970 and has a bit left in the tank once we overclock to catch up to a stock GTX 980. Alas, that more expensive card (around $80 more at the time of publication) is indeed a stronger card, and its overclocking prowess goes hand-in-hand with its nearly-linear overclock scaling. Its 20% core overclock and 11% VRAM overclock combined for an amazing 17% boost in gaming performance, far more than the identical overclock returned on the GTX 970. That shows that the GTX 980 truly is a stronger overall design than the GTX 970, and in our opinion, than the R9 390X as well. May things change in the future, particularly with the advent of DX12 games? Yes, they might, but it's harder to buy for the future than it is to buy for the present, and as it stands, the GTX 980 is faster than the R9 390X once overclocking is taken into consideration. There's just no way an R9 390X, even with a massive over-volted overclock, could close the gap on an OC'd GTX 980. As an aside, while we didn't test it here, we can assure you that the Radeon R9 Fury, which sells for just a bit more than the GTX 980, is in fact even faster, as we found in our in-depth Fury review. There's always a bigger fish, after all! For this roundup, however, we decided to stick to sub-$500 cards, but in the future, we may look at the Fury, Fury X, or their successors, so stay tuned!
As it stands as of March 2016, we'd call the ~$330 matchup between the R9 290/390 and the GTX 970 a draw, while the ~$420 R9 390X and the ~$500 GTX 980 sit in both different price and performance categories. In terms of bang-for-the-buck at reference clocks, the R9 390X is the victor, especially at 1440p, but while many Radeon cards are sold at reference clocks, few GeForce cards are. With the average GTX 980 featuring a 100MHz factory overclock, with headroom for quite a bit more, it's hard to argue that it's not a faster overall card than the 390X and justifies its higher price tag. As we mentioned in the 1440p summary, however, once you get above $500, you find the truly great 1440p offerings, like the R9 Fury 4GB and the GTX 980 Ti 6GB.
Need more advice? For our take on the best GPU picks at every price point, see our Video Card Buyer's Guide, updated quarterly!