Hi David,
I pulled these specs from 2005/06 & 2006/07 brochures that I still have.
The change to the MK3 panel increased the contrast ratio to 1200:1, the refresh stayed the same at 8ms but of course the biggest change was the move to a 1080p panel along with the beosystem 3 engine driving it.
As per my earlier post about the MK2 to my eyes (which are very good by the way) at approx 3m from the screen there was not a lot between the two with a HD 1080i source apart from the MK3 was a tad brighter & obviously the contrast was improved.
Everyone will see things different but let your own eyes & pocket decide.