Wide Format Photo Printers Superb Printer - Expensive Inks And Papers Clarity When Printing Out Digital Photos On A Large Format Printer (mega Pixels Question)?

Clarity when printing out digital photos on a large format printer (mega pixels question)? - wide format photo printers superb printer - expensive inks and papers

I have a Mutoh large format printers. Prints up to 4 meters wide. When printing photos were taken with a digital camera is, what is the difference between 5 megapixels, 10 and 20? In the past I've read that anything over 5 megapixels is not noticeable, but if they are to be enlarged to poster size, there is a noticeable difference?