Anybody fitted 2x Ultra Speed drive quads in a 5810 workstation and does it work?

I have one fitted already with 4x 512Gb NVMe's (so it has the bios/mb support) but I need to increase the storage. I'm going to upgrade these to 1Tb 970 pro's but I don't want the old ones lying about unused.

I'm wondering about the way it divides up the PCIe lanes and whether fitting two of these cards causes complications.