To answer your question, I absolutely love my 850. The picture quality is incredible and haven't really seen any better. It does buzz and I hate it when the volume is low. I sit 15 feet away from the tv and it is clearly audible. Other than the buzz, it's fantastic and not enough to warrant me to do anything about it.
All that being said, if were you, I would go for a newer model. You wouldn't be getting top of the line, but I think the tech in the mid lines is probably comparable or better to the top of the line from 3 years ago. I'm sure you could get close to the same price for something newer, particularly this time of year.