Recently I switched from a pair of GTX 760's to a pair of R9 290's after the stellar performance a single R9 290 gave me in my games, only to find that crossfire support in the latest AAA games is disturbingly inefficient or bugged. The 2 games I play on a constant basis are Far Cry 4 and Grand Theft Auto 5, and these cards don't seem to scale whatsoever.
My system specs are an i7 920 @ 4Ghz, 12GB 1600mhz ram, Corsair HX1000 PSU, and an ASUS P6T Deluxe. At first I thought my CPU was bottlenecking the cards, until I had a friend bring over their pair of GTX 970's and everything was completely smooth again, even in CPU intensive spots like Banapur in FC4. Never went below 80FPS. GTAV ran like a dream and never fell below 70FPS with every setting maxed. In every card switch, I did complete reformats with the latest drivers for both camps to make sure driver conflicts were not an issue. It seems nvidia's focus on eliminating CPU overhead is leaving much to be desired from AMD's drivers, especially if they're leaning on DirectX12 to solve their problems in this regard.
As a new multi-GPU customer from AMD, I have to ask, how long on average does it take for this company to actually fix the problems in their drivers and get proper working profiles implemented? Far Cry 4 has been out for 6+ months, and if this is the kind of support and performance I can expect even after Windows 10 drops, then I think I've made a horrible mistake switching to AMD.