DPI questions for large scale prints

[nmajmani]

So I've got an inquiry for large scale printing, specifically regarding DPI. The basic problem is that I'll be doing a project on movie posters, and I was wondering what the suggested/ best DPI is for printing at print sizes up to 27x40 in. (Standard Movie Posters in the US).

Normally I set prints to DPI 300 for 8x10/ 9x12, but I've seen lots of conflicting opinions on the net about DPI for larger sizes, with suggestions ranging from as low to 50 DPI to the standard 300 DPI. Essentially, what's your experience with printing at such larger scales, and what do you suggest for when I design these posters over the next few weeks.

Many thanks in advance.

[OsmosisStudios]

Here's the thing.

For graphics work (pamphlets, business cards, etc), most of the places I've dealt with have asked for 600DPI files; thats because im making them from scratch.

For photos, DPI is meaningless and PPI (pixels per inch) is more important. If you're just doing a single photo at 27x40, you could get away with 100pixels per inch, and maybe as low as 75. The more the better though.