Ok, I had a moment to take a look at the PDF export and to compare with ID and QXP after exporting your page-sized images at 300 dpi TIFFs.

If I use the PDF/X-3 profile from XDP using JPEG compression set to 100, I get a PDF of a bit over 5 megabytes. Using my PDF/X-4 profiles from either ID or QXP, the PDF tips the scales at a skosh over 6 megs. If that is not enough pages for your book, I would recommend finding another printer.

I have no idea how many pages you plan on having, but you can do the math. You'll be limited to about 66 of these types of pages to remain under 400 megs.

BTW, the optimize for fast web viewing means little to file size and has no result on the quality of the PDF. It's an XML instruction for how modern web browsers will load a PDF in the browser. It's a couple bytes of info is all.

Mike