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Lexigraph has always used the term "Optimized PDF" with respect to our pdfExpress products. We take it to mean that unique Cos object appear exactly once in the PDF file. We use this term in the context of combining multiple PDF files into a single output file. In general this reduces the file size significantly.
However, this has nothing to do with RIP performance. Virtually all RIPs convert each page, one at a time, to PostScript - expanding all images, etc. in-line prior to the PostScript interpreter seeing them. Thus even if Cos objects are shared across multiple pages the benefit of the sharing is lost with respect to RIP time.
I proposed in the CGATS meetings that PPML/VDX simply recognize such structured PDF files and cache objects with multiple references for reuse - simple and effective. However, this approach was voted down.
In general, the only RIP optimization you can do at the PDF file level is to make sure all the images are no larger (in bits) than they need to be. Empirically over the last few years we have determined that most other PDF RIP optimizations are a waste of time.
If you need better performance than you are getting with raw PDF files you will need to reorganize the job to use whatever vendor specific caching your printer supports.
Todd
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