As Alpha says, if the car is unsafe or the owner is a dousche....stick that crap on the dyno. If the car is solid and you want real world loads / conditions, put it on the street to start and get it close. Then fine tune on the dyno with IG and cam gears. If you own a dyno dynamics dyno, or something with a brake that you can set the loads (and know how) then put it on the dyno. Touch up things at the track afterwards. Go thru logs and touch up, etc.

But what do I know, my car only went 152 and I haven't had it on a dyno in forever.