I have one box with SLI 980s, an x79 platform, and since SLI doesn't really appear to help AH much, I disable one card and just play with a single 980 (sometimes) - I checked out doing the same with the latest Alpha client last night, and with a single 980 I had everything cranked in 1440p w/Gsync enabled, and every setting maxed except environment, which is at 1 notch, and avg fps were I'd guess in the 90s, at times up to the max of the refresh rate of my panel (144hz online, 100hz offline in AH3), and some times down in the high 60s, but nothing lower than that. At 1080P where most players will likely play, including me due to the target sizes being easier to hit, so far the Alpha plays fantastic with a single 980. I'd played the first client with sli 970s and they were great too.
IMO so far a 970 will do the trick, Skuzzy has stated as much too, and I'd bet the new 960ti will too.