I have a Pro and standard, and I use the Pro with a 1080p display. I think the difference is noticeable, but I think you really need 4k and HDR screen to make the best use of Pro benfits on visual side. However, for me the Pro really shines on solid framerates and frame pacing. it is overall just much more fluent, and I see the biggest benefits there, and I definitively recommend it. And also it is so much more silent than original (dont know about slim)
Now that I have had the opportunity to play various frameratestrategies in games like Tomb raider, it is my conclusion that human eye is really sensitive to variations so playing at higher than 30 hz but unlocked is not as smooth as locked 30 Hz.
My TV has about 36ms input lag (measured with Leo Bodnar device), and I am not moving to 4k before the input lags come down. I definitively want to have sub 30ms, preferably sub 20ms in my next tv.
So my recommendation is tha Pro is good, but if you want 4k and HDR, make sure you have buy low input lag tv because that is most important in action games. And always hook up directly PS4 to TV. I had an amp in between but after Leo Bodnar device test, I switched to direct, and actually I noticed improvement in Destiny.
