So really the bottom line is that on a stock car, IF you can avoid detonation (doubtful) you really get no benefit from advancing past 14.5* at the crank - past that you are oversparked or getting detonation and not realizing it.
Aftermarket heads and it's another story - they will change the entire ballgame as far as spark is concerned.
The SCT Pro Racer's tuning manual is a great source for this kind of info.
With aftermarket heads, you just advance timing until it pings, then back off 2* - or if if power does not increase - and I'd consider a power increase like 4-7 RWHP per timing degree... if it's only 1-2 RWHP, then I'd back it off a couple.