Many thanks for the feedback.
I'm scanning at 300dpi from a high quality magazine copy. I have an image at 1.45MB which is a little better when you zoom in but not really noticeable at basic HD resolution.
The biggest question I have is what resolution to save the final version as? The original merged image is about 4K wide and is only slightly better than the 348k image above.
Only another 120 pages to go and I'll have this issue ready