I am using even a weaker card than the weakest you mentioned. My GTX 860M with ONLY 2GB of vram is doing pretty well in DAIN Alpha 1.0. I'm processing ~3K footage now (2234x1560px) and it's handling it fine. I only have to use some X-Y slicing (currently 4 slices on X and 4 slices on Y so 16 individual segments with 100px padding). Havent noticed any tearing so far.