My friend has AL l98 heads that was milled to hel and back. Even had to shave the intake to line up. My guestimate is aprox 12.0:1 compression. He only uses 92 octane pump gas. The end of last year it ran 122mph (1/4mi). Have been tuning his car for over a year. He shaved the heads 3 times or more since we met. The car started out with 38*, it loved 38-39*. Even in hot weather. Now, the car will detonate with anything more than aprox 33* total timing. This is all WOT stuff. I raise the advance up until it "pings" and then back it off some. *That's not something for the noob to try!!!* Better have a good sense of detonation when pushing the limits.
On the other hand, idle and part throttle will like more timing. For example, idle might like 20-30* of timing...Keep that in mind. There is tweeking to be done, even with a 1/2 point increase.
