Help deciding on TV

[Intamin]

Well, I'm looking at purchasing a new TV, have read the reviews, know the pros/cons of the sets I"m looking (except for the two bottom of the line Samsungs), and basically need help deciding based on price/performance of those with experience on these sets. The sets are as follows

Samsung pn50c550 1099
Samsung pn50b650 1399
Samsung pn50b860 1579
Samsung pn58b550 1475
Toshiba 55sv670u 1559

I currently own a plasma and do enjoy. IR has never really been an issue, and I have the burn in disk. My main questions are, does anyone know anything about the quality of the 550s with respect to the 6 and 8 series? The only difference I saw on the website was contrast ratio. I'm having issues on deciding if I should get the bigger screen, or get better quality (if there is any perceivable difference). Another question I have, is will the Toshiba have a better PQ than the plasmas when sitting dead on (I know it suffers greatly when off angle)? If this is the case, I may be swayed to get the Toshiba out of my own selfishness for sitting in the sweet spot . Finally, is the buzzing on the Samsung plasmas really that bad, or not noticeable? Thanks for any feedback!

Oh, and I ruled out last years models of Pansonic plasmas, as well as this years, due to the rising black levels and no fix in place for it.