i would say advance the ignition timing 8-10 degrees, you have to run 91+ octane when you do this. you can do more, but it starts to get risky on shity ass pump gas, i think that you can advance up too 15 degrees, but i personally wouldn't. i've had mine that advanced, but i was running on 91+7 point octane booster, that got expensive, hauled ass tho!
I ran mine at 13* when I had my '93 XE. 10 plus or minus 2 is what it's supposed to be at, so 13-15 is pretty safe but the higher you push the degrees the higher octane you need to head off detonation, not to mention the difference between 13-15 degrees isn't going to make a significant change in TQ/HP. So I went with 13 to be safe.