Thanks to the information provided to me, I now fully understand all aspects of LED lighting, and I very much appreciate the help. With this, I will take a closer look at the various 4k TVs I'm considering, and judge the displays with a little more discerning eye. This can really matter, as I would now like to keep any TV I buy for around 4 years to justify its price.
I've read about the Panasonic, and it certainly looks very interesting. I currently own a Panasonic plasma 3d TV (58" VT25), and although it's not the equal of the ZT60, in its own right it provides a superb 1080p picture. At least from my experience, Panasonic makes very high quality TVs, and so the idea that I might be able to get their FALD model for a price that may be close to my budget sounds interesting. Unfortunately, there may be two negatives here. First, if I'm lucky I might be able to see that TV in our largest city 130 miles away when it becomes available, but otherwise it would be a blind buy. Secondly, I'm not sure if I'm remembering correctly, but I thought I'd read that that TV does not have 3D, which I really want.
Right at the moment, it seems my best bet would be to buy the best edge-lit local dimming 4k TV I can afford, accept the limitations, and in four years step up to the more refined and affordable OLED system. I'm going to have to check on this, but as far as Sony is concerned I believe this would mean buying the 65" 900c when I believe it will sell for around $3,500 this Holiday season.
As for the Samsung 7100/7500 UHD TVs, I've seen these demonstrated and I was very impressed. They provide a surprisingly good picture. And as I've said, the JS8500 SUHD is a noticeable step up. However, I'm reading about quite a number of problems the 8500 seems to be having with lighting issues, so I'm getting a few uneasy feelings.
As for Sony, at the moment I'm thinking that although the 900c officially isn't HDR, its triluminous display may be quite close, and aligned with 4k Blu-ray may provide the great picture I'm looking for. I just hope it won't have significant edge-lighting problems.
For the record, the reason I'm waiting until late in the year to buy is because only then will I be able to sign on as a new customer with DirecTV, the first 4k Blu-ray players should be released for sale, and 2015 4k TV prices should come down. And so I'm doing as much research as I can through the year to try to make the best buying decision possible for my situation.
Thanks again for everyone's advice and opinions.