I think the "dpi" in the Carrara output settings properties window really means "ppi". We use 175 line screen frequency for our 40" Lithrone offset press. I just figure on setting the render to 300 ppi (dpi in C) and times the inches by the ppi to get the width & height numbers to set. (I.E., 300 ppi x 8" width = 2400 ppi for width etc.). I think 300 ppi sounds a little high for medium screens (133-150) but I find that carrara exibits some "strange" jaggies when rendering certain angels. Better to start a little higher & reduce down to help minimize those potential problems.