Depends on the image content...for portraiture your best bet is probably a target output of 240-300 PPI using Bicubic Smoother. And then sharpen based on the image. For images with a lot of micro detail you may have to do move selective sharpening but you should still be able to pull it off, depends on the original too. My prefrence is to do final editing on an image that is sized to output, and the bicubic smoother option is very very good. BTW are these 30X40 or 40X60?
Julian Mussi