Eh, I did not forget tolls. In fact I explicitly mentioned it in my post. In comment number 1.

How could you miss that?
However my math was wrong, presupposing tolls constitutes 50% of the tax income in the income screen this means that "tax" income for reformed will be 100d in my example, normal tax will decrease from 50 to 45 d while tolls will increase from 50 to 55.
EDIT, Eh, wrong again. Since trade tariffs (and vassals and manu income) are included in monthly tax income one cannot say that 50% of the tax income is normal tax income and 50% trade taxes, some % must belong to tariffs etc. And census taxes is something else that is influenced of the tax bonus/malus for prot/reformed making the equation even more complicated.
Perhaps you can say that if pure trade income constitutes say more than 50% of your income reformed should be the religion of your choice. But these percentages varies in the game. Early on trade income is nothing, then somewhere when reformed becomes a possibility your income from trade sky rockets. Then later on when you are in the end game (presupposing you are WCing) tax and production closes the gap.
And for WC catholic is definitely better for a lot of other reasons. But that becomes another question.