So this is something you should look at if you haven't already. There is no real straight forward answer unless I reply "do what works for you".
Read this and when reading take note that it's behavior is conditional depending on several conditions. Hope the read helps:
Detail
Optimize RGB Transparency
The Optimize RGB Transparency option corrects color errors that can occur in jobs that contain transparent RGB or Lab objects.
Optimize RGB Transparency affects jobs with the following characteristics:
• The job is in PDF format (submitted to the EX/i Print Server as a PDF file, not submitted from an application
through a printer driver).
• The job contains transparent RGB or Lab objects. They might be objects that you specified as transparent using an application that supports this capability, or they might be objects with a special effect, such as a drop shadow, that uses transparency to achieve the effect.
• The transparent objects overlap, creating an area of mixed color.
If you turn on Optimize RGB Transparency, the EX/i Print Server uses the correct RGB source profile and rendering intent when converting the overlapping RGB colors to CMYK during the PDF-to-PostScript conversion. If you turn off Optimize RGB Transparency, the area of overlapping colors might print with incorrect color or undesirable artifacts.
For the EX Print Server: When Adobe PDF Print Engine Preferred is turned on, the EX Print Server does not convert the PDF job to PostScript when processing the job. In this case, the effect of Optimize RGB Transparency is to recognize blending color spaces in the job, which can improve output for some blend modes when RGB blending color spaces are used.
Optimize RGB Transparency can result in a longer processing time, especially for variable data printing (VDP) jobs that contain multiple individual PDF pages. We recommend that you turn on Optimize RGB Transparency only when necessary to achieve correct color output.
You can specify Optimize RGB Transparency for a job in Job Properties in Command WorkStation, Hot Folders, or a virtual printer, but not when you print from the printer driver. The Optimize RGB Transparency option does not appear in the printer driver because jobs printed from the printer driver are always submitted to the EX/i Print Server as PostScript jobs, which are not affected by Optimize RGB Transparency.