As you've obviously already noticed, trying to set the compatibility in the export dialog to Acrobat 8/9 (PDF 1.7) fully disables any PDF/X standard setting.
PDF/X-4 is based on PDF 1.6. There is nothing that you can do with PDF/X-4 that needs any version of PDF beyond PDF 1.6. In terms of any other new PDF features that are specific to PDF 1.7, such features such as enhanced security features, multimedia support, etc. are irrelevant to and for that matter not allowed in PDF/X-4.
Thus, if your intention is to provide a press-ready PDF file that also displays well, but without any navigation or multimedia gizmos, then PDF/X-4 is the way to go and there is absolutely no advantage to using a newer PDF version.
Thank you for your quick response. I should mention that I do not require meeting a standard. My final deliverable is printed in house, with our own stringent color management, and quality control process.
We are however interested in the possibility of using PDF's for more "on screen presentation" down the road, and are interested in what additional features we may be able to retain with the 1.7 version.
Are the "navigation and multimedia gizmos" the only advantage? Further research led me to limited information about....
"Increased presentation of 3D artwork; XFA 2.4 rich text elements and attributes; multiple file attachments (portable collections); document requirements for a PDF consumer application; new string types: PDFDocEncoded string, ASCII string, byte string; PKCS#7 with SHA384, SHA512 and RIPEMD160", "256-bit AES encryption; incorporation of XFA Datasets into a file conforming PDF/A-2; improved attachment of Flash applications, video (including Flash video with H.264), audio, and other multimedia, two-way scripting bridge between Flash and conforming applications; XFA 2.5 and 2.6 rich text conventions".
It looks like everything new is focused on the multimedia features now included in InDesign CS5.5, with some added encryption functionality.
Thank you again for helping me sort through the information and to understand this better.