Along a similar line - I have been using Genuine Fractals Print Pro for years. I usually print on 13 x 19" paper. There are times my images have been as small as 2200 x 1600 pixels from Vue. You can work with downsizing your image and then making it larger if necessary. In GFPP you can work with a sharpness slider also. I have mine turned off. I am very picky about details and colors. I reviewed it when this version came out.
http://www.perpetualvisions.com/renderosity/review-gf5printpro/review-gf5.html

This program has been wonderful for me, and I've mentioned it before in this forum.