I should've said that 144 guarantees to outspeed all Azumarill and Mawile-Mega. Rotom-W will need to move before both of them for the Will-O-Wisp, and it's a matter of a better safe than sorry speed creep.
As for slashing Pain Split/Rest with T-Wave, eh..I don't think Rotom-W should ever be run without some way to recover lost health unless choiced, obviously. Honestly, I don't see the benefits of T-Wave over Will-O-Wisp either (apart from crippling Charizard), but apparently it's an option that some people take.
44 Speed is all you need, Jolly Azumarill should die out soon anyway as Rotom-W effortlessly speedcreeps it and not being Adamant and max HP is actually a pretty major drawback for Azumarill.