How about 1200 pixels high at 72dpi? They aren't going to print well, but at least we can have a decent look... Even if I was interested in your prints, I would not make a buying decision based on the low quality images you have shown. Are you able to correct the credits for Empire, or are the posters already printed?

By the way, if anyone wants to make some Olly Moss covers, here is what appear to be lossless png files of Star Wars and Empire. There's a Jedi one of equal size but it's a much crappier looking jpeg unfortunately. On one of them "Kurtz" is spelled "Kurts", which probably means these files got out there before the posters were finalized.

edit - new link that includes Jedi. These are not lossless files it turns out, Man_Overboard has vectorised them.