Max xp stacking

[McBain]

x9 on any given day (4+3+2=9)

It's x7, as Whirl said. Again, I think converting to percentages, remembering that 100% is what you get normally, makes it easier to quickly understand.

Week-long 2x = the 100% you already get +100% bonus
3x blessing = +200% bonus
4x elixir = +300% bonus

Excluding double XP events, the most bonus you can have is +600%. Since you already get 100%, your total rate of gaining XP is 700%, which is equivalent to x7.