Well we have turned up the timing upto 21 degrees. My car seemed to like the timing there, the EGTs went down and car made more power. But we turned it back down to 18ish for every day driving. I use 100 octane most of the time. If you are a little scared of the timing you can put in higher octane and it will be fine on the dyno.
I would also start with properly gapped fresh plugs before turning up the timing.