Thief, Assassin's Creed IV: Black Flag, Watch Dogs
Thief can demonstrate an impressive frame rate improvement for Radeon cards when the Mantle is used, but we have no way to capture detailed data with that API so we ran all of the cards with DirectX.
The GeForce GTX 970 takes a strong lead at 1080p. All of the cards manage smooth frame rates but the EVGA card's minimum frame rate never drops below 60.
The 4K resolution necessitates a drop to the normal detail preset, but the Sapphire card catches up to the GeForce here, presumably thanks to its extra memory buffer. The 4GB Radeon card is almost 10 FPS slower.
Assassin's Creed IV: Black Flag
For Assassin's Creed IV at 1080p, we used the highest settings except for shadows, which we set at high. We also enabled 4x MSAA.
At this resolution the result is a virtual tie between the Sapphire and EVGA cards, while the 4GB Radeon R9 290X is left behind.
The leap to 4K means reducing details to high, replacing MSAA with FXAA, setting god rays to low, and choosing SSAO instead of HBAO+. Sapphire's Vapor-X 8GB card pulls slightly ahead of the GeForce here, but only the 4Gb Radeon R9 290X falls behind in a meaningful way.
Finally, let's give the sandbox game Watch Dogs a try. First we''ll use the ultra detail preset, with the ultra texture setting and FXAA enabled.
It's pretty clear that this game favors the GeForce GTX 970, and there's practically no difference between the 4GB and 8GB Radeons.
At 4K, we dialed down the details to medium and turned off ambient occlusion. The 8GB Sapphire card fared a bit better than its 4GB counterpart, but the GeForce retains its commanding lead.