I have zilch experience of £4.5k bikes, but if I did have that sort of money to spend on a bike I’d work almost entirely backwards to your criteria (and to be fair, I’d work backwards with a £500 budget too).
Pick a frame design you like, and ride as many as possible on demo days, even if it costs a bit paying for a days hire of several bikes it’s money well spent if it helps get the right one. Better to spend £500 demoing 10 bikes and keeping it until it breaks, than spend £4.5k and lose half of it in 18 months because there’s something better.
Then put money aside for the fork and shock choices as they’re going to make the biggest difference overall. And a dropper post probably.
Then wheels and tyres as that’s where money spent get’s the best returns.
Then bars, stem, groupset, saddle that you want as those are going to have similar cost per gram saved, and are personal preferences.
Then, and only then, if I’d not wiped out the budget I’d see if I was getting the alu or carbon version.
I’d not buy something off the shelf, because in reality you always end up spending hundreds more tweeking it. That’s a false economy and wastes the first 6 months of ownership fettling!