Eye of the Lord's best uses ...

[Borg]

Is that patrolling bonus of 15 really something valuable or not ?

I would be kinda interested in hearing if you have any tips on how to use units with a "patrol" ability most effectively.

Is it worth it to save "build points" from your Order balance and instead invest them in "Growth" and then Tax your provinces 10 or 20% higher while patrolling them with an Eye of the Lord to keep unrest down, or will this just make unrest spiral up more ?

I reckon, not only can he keep unrest down, but at the same time you also get a continuous search for enemy spies and scouts.
The change from "Order" to "Growth+taxes" should provide equal gold (I hope) while even producing more gold and supplies in the long run.

Order3 gives a 21% gold bonus.
If you raise taxes in your province to 120%,
are we talking about the same amount of gold then (21% to 20%) or is this calculated differently?

If Order3 indeed equals 120% (121 to be exact) taxes, then I think there are some interesting possibilities, or are there any variables I'm overlooking ?