XFX R7750 won't support 60 Hz?

I have an XFX R7750 hooked up to a new Dell U3415W (widescreen, 3440x1440).  The system is Windows 10 x64, running Radeon 17.4.4 drivers and has the drivers for the monitor installed. 

 

Here's all the info, in the requested format:

  • AMD Graphics Card
    • XFX R7750
  • Desktop or Laptop System
    • Desktop (Gateway)
  • Operating System
    • Windows 10 x64
  • Driver version installed
    • Radeon Crimson ReLive 17.4.4
  • Display Devices
    • Dell U3415W, HDMI connected
  • Motherboard
    • Acer motherboard from Gateway (proprietary)
  • CPU/APU
    • i5-2320 CPU

  • Power Supply Unit  Make, Model & Wattage
    • 300W
  • RAM
    • 16GB

 

According to Windows, the card is driving the monitor at 50 Hz, but the monitor's native refresh rate is 60 Hz.

 

monitor.png

 

It seems like the card should be capable of driving the monitor at the correct refresh rate - is there some setting that will change this?