Default Display size

Hi, I have a Sony Xperia Neo since 2011 and I'm thinking about getting a new phone. I was searchin about Sony Xperia Z and Samsung Galaxy Note II.
Besides the obviously better hardware, I am looking for a bigger screen to read books. So, my question is, there is a lot of difference to read in a 3.7" screen (NEO) to a 5"-5.5" (Z,Note II)? Does reading on a phone impair sight, and does a bigger screen reduces this damage?

Also, about the phones, Z and Note II, they are worth?

EDIT: Can someone confirm that the Sony smartphones still can't flash kernel from CWM like the Samsung do?

Thanks