USB Bandwidth

I am trying to encode h.264 video using the Panda and a Magewell HDMI capture board (uncompressed / USB 3.0). This of course works fine on my i7 laptop, but I can only get a max 1280x720 resolution (not 1920x1080) on the Panda. The CPU is under 50% so it's not CPU bound and I'm using the HEVC encoder so it should keep up (using FFMPEG). Is there anyway to speed up the bus? Has anyone tried anything like this with the Panda?

thanks,
-mark