Mega Absol has a maximum speed of 361 and 438 attack.
Night Slash vs Sucker Punch
Also Sucker Punch has 80 base-power while Night Slash has 70 base-power, but if Sucker Punch fails, it can cost the game and you may lose.
Since Sucker Punch is used for slow Pokémon and for outspeed them when having low HP, I think Night Slash should be better or Knock Off that takes off the item and ruining the strategy of the opponent.
Both attacks receive STAB.
Play Rough vs Psycho Cut
Psycho Cut has a 70 base-power and critical hits land more easy, deals with Fight/Poison while Play Rough has 90 base-power. For you get a critical-hit you need lucky, even with the critical-increase.
Play Rough has more power and is very used in competitive, is fairy-type and deals with Dragon/Dark/Fight.
Play Rough has more power and deals with more types.
Mega-Absol can't hold items such as Razor Claw, so that's bad.
Both attacks don't get STAB and deal with Fight Pokémon.
Hope this helps.