TV broadcasts are not in 4k. So if your Comcast cable box is sending a 4k signal to your display, the box is doing the upscaling. In general, cable boxes do the worst job of upscaling. Can you change the cable box settings to have it send the native 2k signal (720 or 1080), i.e., set it to Passthrough? IMO, the problem is Comcast cable (garbage in - garbage out). Cable TV will never be as clear as streaming on a 4k display.
I switched from Verizon Fios to YouTubeTV a while ago, and saved money in the process. You might want to consider doing the same (or some other streaming option instead of cable). I assume if you stream with the display's internal apps, it looks much better?

 

In addition to what @BillP is saying, there is also the magnifiying effect of the larger screen size. Both TVs may be 4K, but those pixels are bigger on the larger screen so any image defects are enlarged as well.

 

Bill/Rolls. Thanks for the feedback. I will investigate further. I haven't tried streaming yet. Someone told me, that multiple devices upscaling (ie. cable/dvd and tv) was better. Are you sure that redundant upscaling doesn't make a difference?

If i use apple tv to stream will that be the limiting factor?

I thought about buying the 65 inch sony because of the point rolls made. I worried that i made the wrong choice.

 

It looks like my version of x1 cable box isn't 4k. The max output is 1080p 60hd. So, that means the tv is performing the upscaling and there isn't much I can do to improve it?

 

Yes, although that is preferable to the cable box doing the upscaling. Let your expensive TV upscale it and keep it on 1080. Some channels are likely 720 and there isnt a whole lot you can do to make that look good. Make sure you are viewing the HD channels too as there are non HD duplicates or at least used to be when I had cable.

 

Samsung processing/upscaling is definitely not as good as Sony. One way around it is to buy an external streaming device (Chromecast, Roku, NVIDIA, Firestick, Apple TV, etc), and switch from Comcast to YouTubeTV or HuluTV or Apple TV, etc, etc. You can then use the external device to do the upscaling, minimizing the processing that the Samsung display has to do. I use YouTubeTV, and get all the local channels through it (I assume you can get the local channels through Hulu and Apple as well).

 

So, Apple TV upscaling is better than Samsung?

 

You can try it and see what your eyes prefer. It's supposed to be decent but don't expect miracles with lower quality content. That would be another input source though and not something you can run your cable box through as a scaler though. At least that is my understanding.

Get a trial of the YTTV while you are at it.

 

INMO, DTV has a cleaner signal. It's still 1080i but has fewer artifacts than cable. I output the signal in its native format, send it to a Darbee, and then allow a Denon AVR to do the upscaling to 4K. It's not perfect, but it's very good for a lot of content.
My $.02