sumeetbadshah29 :
bro what must be the criteria for choosing cpu between single thread performance and multi core
I look for a good balance. The i5-8400 offers good single thread performance and excellent multi-threaded performance for the price.Some lower end processors can do better in single threaded performance.
As far as gaming is concerned. Games which can only use one or two threads aren't very demanding. They were and still are designed for much slower processors which don't offer anywhere near the performance the i5-8400 delivers at 4Ghz (turbo boost). On heavily multi-threaded games. You are pretty well limited to a more expensive i5 or i7 consumer CPU to do any better. Unless you spend a lot more for a prosumer/workstation grade i7 or i9.
As far as the benefits of any of those is concerned. You'll only realize them in games at 1920x1080 with a high end GPU on a 144hz monitor. 4K is simply too demanding on the GPU to see much of any benefit over an i5-8400. I'm sure there may be a small handful of exceptions. But your monitor is only 60hz so anything over 60FPS will result in tearing.
Something like an i5-8600K or i7-8700K would be good if you streamed or did other multi-tasking while gaming. They'd also have a longer useful life. For pairing with a 3080 Ti or whatever numbering nVidia uses a couple generations from now.