Are there any particular genres of game you prefer to play? Are you hardcore into CoD or WoW or is it more general?
If primarily gaming, what sort of secondary tasks do you intend to use it for?
edit: Regardless, this would play pretty much everything out with good performance:
My basket at OcUK:
Total: £2,516.77 (includes delivery: £0.00)
Included a 34" Ultrawide OLED, an ultrawide might not necessarily be ideal for the games you play but it's a preference of mine and I own a variant of the monitor I've listed. A more traditional resolution OLED such as a 27" 1440P can also be had for £400-500, or you may prefer to opt for a non OLED for whatever reason, I will say that OLED will give you the best image quality out of current monitor tech.
I've listed an M-ATX setup as again that's my preference, you could build a standard ATX for similar money.
There is the odd saving to be had here and there, but I wouldn't say it'd be worth it as you've a very healthy budget.