LCD Flat screen techlonogy: Value vs Ultra Sharp

Hi there, this is my first post...

I am in the process of making a business decision to replace 450 CRT monitors with LCD Flat screens.
We are a Dell house and will go with the 17" ones.
The question still unanswered is whether to go for the "Value monitor" or the better quality of the "Ultra Sharp" model. In my research this far I have found the differences between CRT and LCD widely commented on.
What I seem hard to find is the medical reasons on why to opt for the Ultra Sharp rather that the Value model. How mush softer would the Ultra Sharp be than the Value ones
on the human eye, is the one is just a bit sharper that the other.
The technical reasons is fairly obvious.
Any help will be appreciated
Many thanks
Nuka
South Africa