Thank you all for your feedback. I think I tried just about all the suggestions without any noticeable improvement but a simple upgrade to 0.92 was what fixed the issue in the end.
Thanks again for the help.

Hi all, hope this is the right place to ask. I have created a number of files in Inkscape that, when I save to PDF, render very slowly and progressively when opening in Adobe Reader. They aren't complex files as far as I can see and I am using the default PDF export options (1.5, rasterize 90%, doc ...