When creating my PDFs, under the Objects menu and compression type I have always chosen NONE, because when choosing ZIP it does not compress the file very much and I have always been worried about quality using the JPEG choice. I recently had a local printer ask me why my file for a poster was so large (50 MB). So I tried using the JPEG option up to a level of 10 and I was told the poster came out well (I did not see it yet). But it worries me that if I use that JPEG option the end result could be poor. The dialogue box even says high - low.
Normally before I create the PDF I flatten all transparencies, break apart drop shadows and convert to bitmaps, I convert fonts to curves myself beforehand and choose PDF/X-1a and convert all bitmaps to CMYK myself.
Can someone tell me how far I can go with the JPEG compression and still maintain optimal quality?