RX 480 Crossfire: Underperforming in crossfire mode

Specs:

  • RX 480 8GB Crossfire (Reference)
  • Windows 10 64bit
  • Crimson Relive 17.1.1
  • MSI Z97 PC Mate 1150 Motherboard
  • Intel Core I7 4790
  • Antec HCG 850M PSU
  • 16GB DDR3 1600MHz RAM

 

Issue:

 

When in crossfire or multi-GPU mode, the graphics cards run at a lower frame-rate than when crossfire is disabled. An example is in the SteamVR performance test:

 

According to MSI afterburner, both cards seem to run at 100%. Another benchmark, VRMark,  has a similar issue:

 

AMD Radeon RX 480 video card benchmark result - Intel Core i7-4790 Processor,MSI Z97 PC Mate(MS-7850)

 

The RX 480s perform worse than a similar RX 480 PC. Games also do not run as well as they should do.

 

Any suggestions?