Thanks for the views, and yes, fair questions, and ones I have asked myself. I have an AB9 motherboard which certainly a year ago had the latest firmware, though I should check it again. There has been no tweaking and I am sure the RAM is solid.I use two hard drives of 500 each, one for OS and software, and the other for samples and project storage. I believe they are on dedicated controllers but I have not measured the load. (Not sure how to do that). The computer is only used for Cubase recording, nothing else. I don’t have a virus checker and I connect to the net very rarely.
The only thing that continues to puzzle me is that all of this hardware, software and system setup was fine until I installed Cubase 8. Unless I am really missing something obvious, nothing else has changed. I will try more with C7.5 to see if I can duplicate the problems with that version as I certainly have not seen it there yet.
However, I very much see your overall point that if no-one else is seeing this then it is clearly something particular to my system, and I need to work through the possible causes. I have to say though, I am a certainly confused about it all!