This question... again.
My Kuro 9G which I paid like $400 for back in 2012 broke last summer and my insurance company replaced it with a B6 OLED for a $200 charge.
the OLED is 5" bigger, much better design etc but the picture quality upgrade is minimal at best when it comes to 1080p SDR content. My Kuro was modded so the black levels were already so ridiculously close to absolute 0 nit (I think it was like 0.0001) you honestly couldn't tell if the TV was on or off in a pitch black room and the contrast appeared to be infinity minus one. Brightness was absolutely sufficient in a dark room, so for dark room viewing the difference between a B6 OLED watching a blu-ray, streaming Netflix, watching Youtube, watch Satelitte/cable TV and a 9G Kuro is not very noticeable. Colours are both extremely close to the D65 standard.
However with the wider P3 colour gamut, 4K resolution, HDR, 10 bit content the differences become more significant. This represents <1% of my viewing.
So for me the Kuro is more than good enough as I don't have it in a bright room (which would really suck!!) and because 4K/HDR isn't the norm for me just yet. so $300 for a used Kuro or $1500+ for an OLED the choice is obvious where I'm from.
In my case it was $300 for a 9 year old Kuro or $200 for a brand new OLED with 5 year warranty that was 5" bigger, so I got the best deal in the world.