I did an auto-x this weekend with 20mm hubcentric spacers and no issues either. I have them on ap2v1 to clear a brembo bbk

 

Just to reitterate what everyone else has said I have done a track day and a few autocrosses on extended studs and spacers and have had zero problems

 

High-strength extended studs (ARP) with hub-centric spacers are fine.

Regarding the loss of hub-centric function on the hub side with a BBK or two-piece rotor, you will still be ok. Just go slowly with torquing the wheel down and make sure it has a chance for the lug nuts to properly seat the wheel in the right spot. The wheel will take the hub-centric spacer along with it to the proper location. I do lots of little turns in the star pattern before I actually get them to 80 ft/lb.

Additional track width works similar to sway bars in terms of adding the most grip at the opposite axle, but differs in that grip is added at both axles (sway bars take away grip at their own axle, when all else is equal). So additional front track width will add a small amount of a grip at the front and a larger amount of grip at the rear. All track width increases to grip are relatively small, though.

 

Yes they are fine and I have lots of experience.

Raced with APR extended studs in front and 10mm spacers for years - non hubcentric. Competed at SCCA Runoffs with that setup and even after dropping wheels on the outside of turn 6 at 90mph and then being hit in T11 everything was fine.

Shear load only matters if you don't torque enough. I made that mistake once with my old Mitsu Evo time attack car and the studs sheared off at 90mph. Aluminum alloy spacers expand more than steel and will cause the lug nuts to loosen slightly during the first couple heat cycles.

To prevent it, let the wheels and hubs cool off after your morning sessions then re-torque the wheels to ~85 ft-lbs right before going out again.