I would guess it would be the same as error codes, as you have to go through the branch everytime to check if it's Err or Ok.
At lot of what we learned about performance in the old days is no longer true. I'd say every time I've fired up the profiler to try to speed something up I've gotten a surprise and rarely is it because of inefficient code on my part. (And the only one of those I recall is where I used n^2 routines knowing n was small--only the use had evolved, when I wrote it n was generally around 20 and almost never over 50. When I got asked to look into it there was a case where n was around 2000.)