Hi I did same test with the new game Battlefiled 1.
I did found out when I was just using one card I got around 60+80 fps randomly.
when I turned on Crossfire "enable" I get the same resualts as just one card enable.
Poor Performance on AMD Crossfire.
I'm using R9-390 so there should not be a problem tho I shoulde get about 100+ with 2 card enable.