The duration will depend on many factors when trying to optimize performance as our engines are not real fussy about cams as even a stock cam will easily get into the 10's.
We like to first take into consideration intake air flow and exhaust flow ratios from the heads which are being used to pick a cam as well as HP range, if street or strip use or both, and what have experienced that works well.
Alum heads have awesome exhaust flow as compared to iron heads so we usually do not bias the cam to the exhaust when using them.
A version of the old ATR 214/210 roller cam with our tweaks we have used for years with slightly modified cars, and it has been into the 9's with a street GN.