Frame rates were fine, great in fact - the 1070 and the 980ti were generating significantly faster frame rates than my trusty Nvidia 970 card.
I have a ATI 6950 and an Nvidia 970 that work A-OK on the same screen and in the same PC, that naturally are generating lower frame rates.
I've tried DVI and Displayport connections to no avail, and the latest drivers etc.
Note I am aware of PWM and drive the screens at 100% brightness to eliminate PWM using the video card brightness controls to make things usable.
It's something about how the image is being rendered on the screen by these cards, that at least to me appears to have changed.
Still maybe I need to look into more detail about minimum and maximum frame rates, and latency in general.