"He who marches out of step hears another drum." ~ Ken Kesey
300LPI 80% is what we use, pm me a mailing address and I'll mail you a 4x4" chunk if you want, free. I had a 18" x 24" section output on an image setter so I didn't have to pay the silly prices the padprint supply houses charge for them. Each chunk lasts me about 6 months or so before it eventually gets too beat up.
I had it done at a film output shop that had a true imagesetter, 300LPI is way too fine for any epson or the like.