The post processing on TVs tend to make their response times much higher than even the cheapest monitors.
I don't notice any lag playing on my TV. I only play on my TV. I have the image duplicated with my monitor. But this is 1080p.
My TV in fact has a gaming mode to deal with lag (at the expense of something else I can't remember what), but I've never felt the need to use it.
what model do you have?
I looked into 4k TV's when looking to upgrade my TV.
In fact I done a lot of research on it, and the truth is, unless you want to pay a small fortune I wouldn't bother with a 4k TV yet, all the entry level TV's and some of the Mid level TV's are pretty poor at true 4k.
I also found a nice article that helps with deciding if you actually would benefit from a 4k TV, it all depends on viewing distance and angle, Take a look at this article in regards to this http://www.rtings.com/info/4k-ultra-hd-uhd-vs-1080p-full-hd-tvs
In the end I got the Samsung UE40H6400 Active 3D Smart LED 40"
Because of how big my lounge was, 4k was marginal improvement, and would of been about £800 more expensive to even get a remotely decent one.
Hope this helps!
I would stay away from Samsung TVs and Monitors, they tend to have bad colour contrasts compared to other manufacturers
65" Damn I am jealous, I only just managed to persuade the GF to move up to a 40" form our 32" we had in the lounge, silly thing is, TV design from the last couple years have massively reduced the frame size required to hold the panel. My 40" TV is about the same size as my 32" was as the frame on it was so big!
If I had gone and actually physically seen one in Currys or something I would of tried to go for a 50" instead Maybe next time!