Hi LaLa
There are several threads here in which people have mentioned a difference in clarity and glare, I'm not sure I've seen the word "significant" used, but most people have said that it is definitely improved in the 900 over the 600.
Here's a few of them:
https://www.mobileread.com/forums/showthread.php?t=69602
https://www.mobileread.com/forums/showthread.php?t=68199
https://www.mobileread.com/forums/sho...t=66541&page=2
Hope that helps