I’m not at LL, but Mode S/ADS-B functionality is the same for everybody, I can confirm we(ATCOs) can’t see your selected speed.
However, if you’re doing something different than preceding or succeeding traffic (even slightly different), it does stand out. So if they ask you to maintain 160, and you keep 165, that difference will be noticeable after a short while, if the others are doing 160 exactly.