Depends on what you mean by minimal gains.
If you play online games a lot like Warzone then a really good PC will get you 200+ FPS at 1440p, for example, which combined with a high refresh monitor gives you advantages in FPS games you simply don't get on console.
If you are primarily getting it to play single player games then refresh rate doesn't matter as much but you could then still easily spend 2k+ to go 4k.
Anyway you sound like you've no idea what you want so I'm not sure how we can all help you
the reason you're seeing so many mixed things online is because PC gaming is so versatile depending on what you're after, you really should try figure that out first. What games do you like? What's your ideal budget? How long do you need this to last before building again? Do you care more about resolution or FPS? etc.
The simplest answer I could give you is spend between 1,500 > 2,000 (pounds I assume?) on a solid high end PC with a high-refresh 1440p monitor and that'll cover most bases for you. In most cases it's not worth going 4k because costs then increase exponentially in order to try maximize performance.