CrossFire: Arma III At 7680x1440
When I first started generating CrossFire data (at the request of /u/Schmakk in /r/buildapc), my reaction was, "...the heck? How can a card that offers so much memory bandwidth and pixel fill rate fall behind the card it was faster than in single-GPU testing?" And then I started my clock rate log and everything made more sense. Beyond the possibility of performance being shader-bound, we know for a fact that two R9 290Xes in CrossFire throttle back their clock rate sooner and more severely than one board due to heat.
With that said, two $550 cards are still keeping pace with two $1000 boards in Arma III.
Even with two high-end cards, the Ultra detail preset is a bit much at 7680x1440. You'd probably want to scale back a bit if you own three 2560x1440 screens (incidentally, those 11 million pixels can be had for $1200 or so, which is almost one-third of an Ultra HD screen).
We record higher frame time variance from AMD's cards. The fact that its single- and multi-card solutions are on fairly event ground keeps us from suspecting an issue with CrossFire, though.
