I finally found a solution that works for me so I hope it works for others. My O/S drive is a Samsung 950 pro M.2 drive and windows is installed in UEFI mode. In CSM Compatibility mode I switched boot option to "UEFI only" and set everything else to Ignore. Also Changed PCI-Express setting to "UEFI first". It's all in the same menu so you'll see what I mean when you play around in there.
Cold Boot time is down to around 15 seconds which I'm happy with. I've left all the memory checks at auto and I'm running 32GB @2600mhz in XMP Mode. Bios 1402.
