This is a loaded question, you know.
It all depends on the engine, quality/grade of fuel, and driving style/habbits. Typicaly with high grade 91 you can get at least 12, sometimes up to 15. With good 93 you may have little problem with 15 or never be able to run past 12.
My suggestion it put a full tank of the typical gas you would buy, drive the way you would normaly, take you timing light with you and make adjustments between short drives, slowly working your way up a degree at a time until you get ping, then back off a degree. This can be done in about an hour of drive time, as the engine is getting worked and is warm as you get to the max acceptable timing, you know it is safe for daily driving. I have seen way too may people set the timing up and think it's great until they drive it hard for a while and then get a bunch of ping.