I had exactly that combination M447/M510 on my first bike, and as I got better and faster I found that I didn’t have the confidence going into corners/obstacles that they’d stop me – sort of a time lapse between spotting the need to brake and pressing the levers and starting to slow down (I’m 100kg kitted up by the way).
I replaced them with SLX and there was quite a big difference (and yes, still resin pads and same size rotors – so it was all in the brakes themselves) and I now have much more confidence to approach corners/obstacles fast in the knowledge the brakes will wipe off the speed when needed.
Just my experience, but happens to be with exactly the combination you have, and are looking to upgrade to, and I say – yes, it makes a big difference!
Can’t comment on Deore as I haven’t used them. Have XT on another bike and they’re same as the SLX.