As the generations have gone on, the gap between XT and XTR has got closer and closer IMO. Back when we had M950 XTR and M750 XT, the difference in quality was vast. Moving to M760 and M960 the game changed somewhat cos of the flappy paddle shifters, but up to M970 and M770 XTR was still appreciably better than XT. The last 10spd iterations of M780/5 and M980/5 were closer again, but XTR shifters more than anything were worth the price premium over XT.
The new 11spd stuff however… I’ve ridden both, and honestly whilst I can tell the difference, I wouldn’t pay the premium for XTR even if money wasn’t an issue. The new XT is that good really! New XTR is very heavy and mechanical, a feeling akin to a Campagnolo Record shifter I’d say, it’s very heavily sprung and needs some force to shift it, but the shift is absolutely instant when it goes. New 11spd XT is pretty close to the last gen XTR in feel I’d say, which I loved, hence I’d go with that.
I’m bought into SRAM these days though I’m afraid, because I jumped on the 11spd bandwagon before Shimano decided it was going to join, but also cos I’m sold on their Guide brakes and Reverb posts and I like how it all integrates together nice and easily. If I was starting afresh though, would probably go XT shifter and mech, Hope Tech 3 Brakes and that new Raceface Turbine dropper post.