What type of printing are you doing? I recently had an 18" x 24" print made at Kinkos for a friend. I used the 72 dpi resolution that is standard, and simply cranked up the pixel rate to the highest setting (4090 or there-bout). The print came back looking incredibly sharp. I was definitely pleased (as was my friend). Try it once and see if it will work for your purposes? Might save you some headache (and render time). Good luck.