Max xp stacking

[McBain]

My post came from a dev a long time back. I have no clue where to find the original post though.

You may have remembered that incorrectly, see below:

Say the base XP you get from an NPC is 1.

A 4x multiplier will multiply you base by 4: 1 base XP + 3 additional XP, for a total of 4 XP.
A 2x multiplier will multiply your base by 2: 1 base XP + 1 additional XP, for a total of 2 XP.

So, now let's look at how these work together.
A 4x multiplier plus a 2x multiplier will add the benefits of both of these elixir to you base XP: 1 base XP + 3 additional XP + 1 additional XP, for a total of 5 XP.

The above describes stacking a 4x with a 2x for a total of 5x. If you add a 3x into the equation on top of that, it becomes 7x. The key point is that your "base XP" does not stack, only the benefits of the elixirs.