From Nsh's post:

Database size [...] is only one of the factors that affect accuracy, there are many others. And there is no direct dependency between size and accuracy. It's possible to have good accuracy with 70 hours, it's possible that with 10 thousands you'll have bigger error rate.

Here on page 13 you can find comparision of accuracy and database size

http://mi.eng.cam.ac.uk/research/projects/EARS/pubs/evermann_sttmay04.pdf

Basically the difference in accuracy between 400 hours and 2200 hours is 2%.