Start with the correct offset wheels on, find a piece of road with no
kerb and grass at the side of the tarmac (and nothing solid near).
Drive along with the inside wheels on the grass. Apply the brakes
(moderately) and feel how easy it is to keep the car going straight.
Repeat with heavier braking if you feel confident. It would be ideal if
you had a G meter in the car to measure how hard you were braking, a
pendulum against a card marked off at various angles would do, but you
would need a passenger to watch it.

Then put the incorrect offset wheels on and repeat, again starting at a
low speed and gentle braking.

What I would expect you to find is that with the incorrect offset wheels
you will feel much more pull from he steering wheel, and that the
maximum you will want to brake will be much less.

Let us know how you get on.

I know of someone here in NZ who had incorrect 17" wheels on, and ended
up going off the road, through a fence, and into a tree (I think).
Certainly the car was a write-off. The driver, and someone else who
looked at the road couldn't possibly see how he had lost it there.
Perhaps if he had the correct offset wheels it wouldn't have happened?

I once was forced to put the left wheels off the road by an oncoming
truck (on a narrow road), and had to brake at the same time because I
was approaching a narrow bridge downhill. I know that in any other car I
would have had to fight to keep the car going where I wanted to as I
cautiously increased the brake pedal pressure. In the 928, it did all
the work for me, and I put that down to having the correct wheel offsets
and hence the correct negative scrub radius.

Smiffy