Thanks guys. User issue - as is often the case. You buy something new, and then you get issues so you blame the latest device rather than your own stupidity. Well mine anyway.
I will display my failing for all to see, such is the punishment I deserve for not testing fully before posting. Over the weekend I purchased Izotope mastering suite and I've just realised - or discovered - that when active, it really does cause latency on my spec. In my limited defence I was just fooled by the odd message from Cubase informing me of new audio drivers that threw me into looking the wrong way after just installing Helix software.
So apologies for wasting your time, but thank you all.