About 150 to 200 dpi are all that most people will ever use for making digital prints. There is not a significant improvement going to 300 dpi. There is a significant improvement going from 75 to 150 dpi.
Most people tend to forget that the reason for making a large print is actually to increase the acceptable viewing distance (change the audience experience). A 4"x5" print is great in a book, but only one or two people can get around the book to view the image at one time. A 4"x5" print makes a really poor billboard! It is hard to see from a moving car. (A different audience.)
Yes you can put your nose on an 11"x14" and claim to see the grain and noise, but is this same thing apparent at proper viewing distance (several feet from the print?) An 11" x 14" print is not intended for hand holding, it is intended to let more people see it from a comfortable distance. Too often I have hear that all prints need to be printed near the best resolution of the printer. To that I say bunk!
I am including a multi-page write up (=>a pdf file<=) that goes into far more detail on how many pixels you need to achieve desired output. You will find it is also based on the "method" of final display ... monitor, lcd, monotone print. color print, etc. Eventually I will update this write up and add it to these WEB pages, but for now you can download it and read it if interested. It describes in far more detail the workings of printers, monitors, and how they effect the final output.