Pjay to report back on your suggestions that I've been experimenting with. I found a major difference between the released x64 LAV and MPC-HC, and the nightly builds of both. So Ive stuck with nightly builds for both x64 LAV and x64 MPC-HC.
I have a video sample that is top end and absolutely kills my 8 logical core i7 CPU. Its 2160P 60 FPS, Main 10 with the 10 bit colour and its level 5.2 on HEVC with some fairly high bitrates.
Using the nightly builds of LAV and MPC-HC, I'm pleased to say even with DXVA 2 copyback I get zero dropped frames or stutter and even have some headroom left in the gpu video engine, the gpu memory controller and so on.
It looks simply stunning on my curved 65" UHD display
Thanks allot for your suggestions now I'm already for 10 bit UHD content on HEVC MAIN 10. I love my GTX 960.