Took everyone's advice from the forum and cranked up the gamma, brightness and gain settings for another attempt at Saturn early this morning with the 12.5" and NexImage.
Poor seeing and really bad wind vibration meant that I only got 650 acceptable frames to stack but it's all about improving from the previuous effort. (Hoping for better conditions tonight)
Have you tried using LR deconvolution processing in Astra Image instead of ME. I find this reveals detail a bit better than ME but also a little more noise.