Probably wrong about this, but I think spellcast can't tell if you have just one march or two up at the same time. Buff is just listed as "March" I believe, not advancing or victory.
Maybe autoexec would work but i'm really not sure.
As there isn't a method to distinguish between Advancing or Victory march, nothing you can do outside of creating a button to change to a haste capped setup and back when buffs wear.
hmmm I guess i have to figure a way to create a button to change to haste cap. I thought I would be able to utilize the ID's on buffs similar to people using codes ie cancel 71 to cancel sneak before spectral jig or cancel 66 to cancel utsusemi....