If you run 14* of base timing, then you will need to run 91 octane, without a doubt. Otherwise you will detonate. Here is the real test. Fill up w/ 91, set it to 14*, and take it out for a spin. Run the car in 2nd & 3rd gear all the way to 5000 rpm's @ WOT. If it doesn't detonate, bump it to 15*. Repeat the test drive. 16* is about the highest you will get w/o detonation.
If it's warm out, you might not get away w/ 15-16. I would try 14* and leave it there if it doens't ping. That seems to be the best timing to run with the most gains. If you advance it too much, you will lose power.
Scott