Thanks for the 2c. That compressed memory sounds like it might have something to do with it. Have tried the manual page size trick you suggested to double the ram 64 to 128gb. Unfortunately no difference although there is only one drive on that machine so there could be a bottleneck somewhere. I've given up though, spent half a night trying to optimise a scene to render out on it but it just snarled up on the first pass after 7 hours. Ran the original less optimised scene on a windows 10 machine the next day and it rendered fine using 80 odd% or the ram according to task manager. When I say rendered fine it was running slower, seemed reasonable to 6 passes then slowed to 3-4 passes an hour but it's better than 1 in 7 hours!
Going to have to admit defeat and get a win 10 license and flatten it.