How to prevent PDF presets to alter image quality

Question

In experimenting with various PDF presets, I noticed that with grayscale images in Photoshop, saving as PDFs using different presets, alters image quality, specifically the contrast. 
Therefore, it seems like saving an image in the "wrong" PDF preset could undo a lot of prepress work. Is there a better way/format?
To get a crude idea: there is an 8.7% decrease in the percent black between 10% and 50% values (the range) on a step wedge between the original in Photoshop and the HighQuality PDF, which showed the same values, and the PDF/X-1a, which compressed the range by 4 percentage points (approximately a 8.7% decrease). 
A visual, and idiosyncratic, assessment of four versions of the same image  (Photoshop grayscale, High Qualtiy PDF, PDF/X-1a, and PDF/X-3), which included a step wedge and color ramp, would rank the fidelity to the original from best, HighQuality, to worst, PDF/X-1a. 
The same grayscale image in Photoshop CS6 was distilled (File > Print > Adobe PDF) to PDFs using unmodified PDF presets in Acrobat XI distiller.
The following composit screen shot (all four images on the screen, screen print, reorganizing them, then reducing the image to a 120 dpi at 4.2" wide (including text) gives some idea of the differences, but a lot got lost getting it here. 
Walton

Answer 1

I do a lot of work with print-on-demand books (design and formatting), and I am active on the CreateSpace (the p-o-d division of Amazon.com). Although CS will accept work in virtually any PDF preset or origin (doPDF, cutePDF, etc.), PDF/X-1a is the recommended format, and for other companies it is the only accepted preset.
Here is the dumb question:
On the monitor (as the screen shot shows) the four images (PS, HQ PDF, PDF/X-1a, PDF/X-4) appear quite different: i.e. my video/monitor system is representing the images differently.
A screen shot of all four images on the screen at the same time, then with the info window open in Photoshop, I assessed their CMYK values in the exact same places on each image (lining the images up, using the measure tool and  guidelines, measuring at high magnification); here (the color original followed by the original grayscalse conversion) are the black values (C00 M00 Y00 K1-100):
The images display differently, and those displays measure differently.
When I view the PDF images, they appear differently, but if i measure them (Output Preview set to Dot Gain 20%) the K values are the same. 
When the same image is prepared using different PDF presets (a previous set of test using different images and looking for something different) they will print (printed in a black & white book by CreateSpace) differently.
How can one predict how a grayscale image will print? How can one prepare it and safely convert it to PDF?
Walton