I did testings few moments ago, and slx now brakes way better then before. Cleaning and brushing of the pads, rotors, calibrating helped. Feeling of XT is more like biting, that I do like and prefer more metal materials of the leveler then SLX plastic without touch of dots. Well, must say calipper itself is better on SLX 7120 and overall set is more controllable and forgiving on the corners while I'm having them on the front. Nevertheless they do brake at least as good as XT for sure. I would change pads to metal ones because it is still not proper comparison. I like the design of new SLX and people say they don't like blue. Well, it's actually more black then blue, just little chemeleon red-blue sparkle and looks blue on pictures. If I had no SLX set just laying around I would not consider changing to the slx of course, just directly to the new 8120. Do not care about what is better, xt or slx.. both works great. Tmrw I would give hard testing to my new bike, with racings, hard jumps, flow corners and hope to survive. After that inspect the breaks and give feedback.
Thank you guys for help here, because I thought SLX would be worse then XT I have.. plus fact my bike is full xt made me sceptical.. After cleaning stuff must say would not go back now, and still curious how things would stand on trails.