have you tried?
300 DPI is a "rule of thumb" - there's no magic here. In fact, 300 DPI is only meaningful for an average sort of magazine; it's way too high for newspaper to use an example.
So the success of printing at less than 300 DPI depends on several factors, including:
- the viewer's opinion of "quality"
- the image (some do better than others at lower res)
- the paper and printing standards (believe me, the same image reproduced in your local newspaper, in People Maazine, in National Goegraphic and in the CocaCola annual report will look mighty different!)
So - try it! 200% you might find you can get away with.