This Aegislash(also copied from Maison thread) runs 79 Speed, so no worries about tying with the 80 Speed group. However, I'm not sure this is optimum for Battle Tree, but I have not had a chance to look at it myself. I remember part of the reason for the 79 Speed was to outrun Regice and avoid paralysis, but a quick switch to Fini and back, will afford another set up opportunity without paralysis woes. Minimum speed would have been useful many times when I had to risk another Swords Dance to ensure a OHKO on a slower opponent without having to worry about taking a hit in Blade form.
Oh yeah, I forgot about using an imperfect Speed IV. I actually used an Adamant 31IV, 4 Spe variant to hit 81 Speed for the Maison, mainly cause I was concerned about hitting Empoleon4 with a Sacred Sword before it could potentially Sub. However, both sets have their merits and should be adjusted accordingly to your team. Definitely looking forward to using Tapu Fini when I get the chance; having an immediate Ice-resist immune to freeze hax is amazing, not to mention Aegi being able to reap the benefits while Misty Terrain is still active.