Start at 10 degrees without the spout OUT. And start increasing in small increments, like two or so. Generally people will say the best is a couple degrees backed off, after you start to get detonation. But the absolute best way is to get on a dyno and tune it there. Then again there is the whole issue of what parts you have. For example the TFS Twisted wedges and AFR like more timing than the GT40 heads..
On a side note. You will need to run better octane as you increase timing. And possibly more fuel pressure.
for the track i run 18* with my afr's but normally around town its at 14. i can feel the difference but like to be more then safe when just daily driving. dont need every bit of power. most will say 13-14* on stock heads but you will have to run 91 octane