Yeah - I went back and reread the initial post (actually the whole thread too), and I agree with Jim, that your 40" display behavior is not normal whatsoever.
He had suggested you try swapping the connections from the computer to the 2 TV's, to see how they each behave using the cable from the other one. That might expose some additional behavior you could post back for us to try to help you figure out what is happening.
The other thing he suggested was that you try using the 40" TV as an actual TV, to see if there are any display issues once it has no connection to the computer. That too may be telling.
I use a 32" and a 40" TV all the time, and have for the past 2-3 years, with absolutely no issues at all, so something seems amiss with either the hardware or the drivers or one of the cables.
Bob Bone