Hisense 65M5500/K5510/N6800
Both are reviewed on this website and both will perform very similar. Improvements to software probably make the new model better.
It depends on price which is the better buy though, usually the newer 2017 models come with a premium. Hisense however do have more competitive pricing on their new models compared to other brands though.
Other option would be the Panasonic 65DX750 if you can still find it somewhere for a good price.
By finding a 2016 model you stand a much better chance of getting more for your money but now isn't the easiest time to buy. Whilst 2017 models are overpriced, 2016 models have all but sold out so are hard to find. Hisense seem to be the only manufacturer releasing their new models in line with reduced prices from the year before. Who knows though, maybe that's because they plan to reduce those prices even more.
About the same as the Hisense M5500/K5510/N6800 probably except it doesn't handle 24hz content without 3:2 pulldown.
Its a problem that is for sure, we are at the time when 2017 models are costing a lot more than their 2016 counterparts, whilst they are not usually worth the extra.
At the same time, 2016 models are hard to find. The 58DX802 you found at John Lewis for example isn't a good buy, but it is still a lot better value than 2017 models which are very overpriced right now.
The Same TV can be found as a refurb on Panasonics eBay refurb store for £800 or even cheaper manufacturer refurbished elsewhere on eBay. Since you want a long warranty though you are going to be limited by the choice of what stores like Richer Sounds and John Lewis carry. Perhaps they have open box models on Richer's clearance section with full warranty? not sure.
So the best thing to do really if you can't find a 2016 model with the warranty you want is just to wait. You will be picking up a lot more TV for your money by doing just that. Right now that 65MU6400 is £1500. Not long after Black friday last year you could pick up the same size 65KS7000 for the same money. The KS7000 is a much, much better TV. 100/120hz panel, UHD premium accreditation for a decent HDR experience and at least some form of local dimming to make those big brights stand out from the deep blacks.
Looking at tv's now, I wouldn't be surprised to see TVs like the 2017 Sony 65XE9005 or Samsung 65QF/C come in to that kind of price range over time.
As for Hisense, the only poor things I have heard is regarding faults in a batch of the 55M7000 model. They are great TV's for the money and really right now obtaining one even as a stop gap until you can buy at the right time in a few years would be better. The 65M7000 is a better tv than the Samsung MU6400 for example and it was available for less than 1k not so long ago, not sure if you can still find one though.
To give you an idea of why a 2017 model like the MU6400 isn't a good buy right now, have a look at the price of last years model over time. If you did want to buy from Samsungs budget line, look at the 2016 KU6400 instead, its £500 less!
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So, continue to see if you can find a 2016 model at a good price or wait until the new models go down in price to get best value!
The N6800 isn't actually as overpriced as some of the other 2017 TVs. Its about £200 more than the M5500 last was which is most comparable to that model in 2016.
The nice things about the new Hisense TVs too is the improved smart platform...but I guess it doesn't matter too much, its always better to use a separate system anyway.
Not sure if you have seen but it was recent reviewed on here: Hisense H65N6800 4K LED TV Review there is a user review submitted by @simoxxx84
If buying from Richer I would also call them first to ask if you can arrange a demo in their designated rooms. Take some of your own content to test it out before buying.
Your current TV is a hard act to follow. In many ways LCD is still two steps forward one back. Even OLEDs now can't match motion performance of Plasma TVs like yours.
The main gain today to be had is UHD resolution and HDR. Both are source dependant and the former you have to view very close to benefit from..although your current TV is 720p so 1080p content should look a little better.
SD content like normal tv channels may look worse.
Overpriced as its a 2017 model, I would look at waiting for the Sony XE9005 to drop into your price range. That at least is a capable HDR TV when it comes to being brighter. You can compare them both here: TV Side-by-Side Comparison Tool X900E & MU8000.
Your current TV is a hard act to follow. In many ways LCD is still two steps forward one back. Even OLEDs now can't match motion performance of Plasma TVs like yours.
The main gain today to be had is UHD resolution and HDR. Both are source dependant and the former you have to view very close to benefit from..although your current TV is 720p so 1080p content should look a little better.
SD content like normal tv channels may look worse.
You could wait to see if more of the DX-902's pop up on their refurb store, or buy the one I posted. I have seen 65DX750's on their too but not as often.
If that is the Philips 7601 then yes thats a good buy, its similar to the DX-902 with everthing, better with motion but not quite as good with HDR.
This is a forum where people come with problems, there isn't one tv you won't find problems with according to people one here. Thats just the way it is. No one really comes on here to say everything is fine and dandy, in fact 99% of people who buy tv's won't come on here at all!
But nonetheless, if you are concerned you could always wait for more user reviews. More importantly if you get it from a reputable dealership, you should be able to return it if you find a fault. No different with Hisense to any other brand of TV.