One would expect that if the 750 were to have some major improvement in PQ over the 650, Samsung would have touted same in their CES press release. They didn't and I don't think their is any difference. Too many on this thread are operating on speculation and suspect or foreign documentation.
Personally, I'm a lot more upset over the fact that TOC is more like Red with a TOB (Touch of Black). Samsung, you had the best looking LCDs with the piano black in 2007. It wasn't broke, why did you mess with it?