[Quoth]

Convert/Export epub to docx or RTF. Open in LO Writer or MS Word. Fix page size, fix styles etc (save between edit sessions as odt on LO Writer, and docx on Word).
Export direct as PDF. Old versions of Word don't have built in PDF export, in such cases install free Libre Office and use LO Writer.
Results are perfect.

Those page choices are for ebook conversion. PDF output on Calibre uses the PDF Output option page, as does docx (but on docx you either pick a predefined size or enter the size in Points, not inches). RTF seems to be fixed Letter size.

You can use a predefined size in docx output if custom box (Points only) is empty.

Any size of A5, A4 (or fixed Letter in RTF) is OK, because you'll set the page size in MS Word or LO Writer to size you want for PDF.