i need a 51" samsung plasma for a client. samsung offers 4... pn51e8000 ,7000, 6500 and 550. when you pull up the comparison on their web site there are 3 pages of about 60 lines and there is NO differences at all in any of them... all the same resolution, contrast, features and all else... there are maybe 4 meaningless elements that are not the same... 1 has an extra usb port, another an extra hdmi... but in a functional sense, they are all identical. the 8000 is 1800 $ the 550 is 900 $ . what am i missing here ? please.