I bought some drill bits and reamers which have two drill sizes in one drill bit.
The forward side is used as pilot and perfectly enlarges in the same hole diameter to the next step.
The reamers are even more precise for updrilling.
I strongly recommend using these on your project for the critical holes like the rear spar wing drlling to fuselage or elevator horns.
In fact I would recommend to use them for all larger size holes.
see this article for pictures:09/12/2018 - Continue F-7114 gussets - 2H