Thank you for your reply, and sorry for the late response i've been on holiday. I ended up using this instead https://codepen.io/cmalven/pen/vqbJPM Content in this situation does need to be duplicated, as if you just move it and the screen has a visible area of 3.5 items and you have 4 you see half of the last item jump from the last position to the beginning. Hope that makes sense.
Okay so as you can see I have built one. I originally used Slick and hacked it about to make it auto advance but it was super laggy and not very reliable. Slick created a good basis (cloned slides etc) so I left that in but disabled the rest of the slider functionality I've then created functions to move the slides with GSAP and re run the function on complete to auto advance the slides. I've also added a pause on hover and next and previous arrows to navigate more quickly. This all generally works but it is slightly laggy on safari (It's okay but if i add text to the slide it becomes hard to read, I've tried creating a CSS animation which is smoother but I can't get the extra features to work) Also I'd need to do some tweaking to get the timing to work consistently with different width items as it's set to a fixed 3s per slide Any help much appreciated, I feel like there may well be a much better way to do this with timelines or something similar