[JLMounce]

My approach is to be overly conservative unless as steve25 has stated, you have the ability to utilize a dyno for tuning.

The way this is done with a dyno is typically in zones, or cell by cell to monitor MBT (maximum brake torque). You sweep through a conservative to aggressive timing curve per cell as the dyno stabilizes the rpm and MAP reading. Typically there is a range where spark advance will flatten out the torque produced at that point in time. For a street vehicle on pump gas, you would set your timing at the low end of that plateau for safety.

As steve25 also mentions, engines on pump gas will typically reach spark knock before MBT, so it's important to be listening to the engine (or knock sensors directly if so equipped).

Based on your original post, if the engine is not showing you any signs of being unhappy, like running hot, pinging, surging or bucking, while also providing good throttle response, it's unlikely that you'll be able to legitimately improve on the tune without a dyno.

If, like me, you kind of have a cruise "route" that you always tend to take, drive that section and you can make tiny changes to the timing by watching you MAP readings. adjust timing for lowest MAP/Highest vacuum. But don't make wild changes at a time. 2* increments at a time an monitor. Same thing with your idle. Start with your idle fueling and adjust for lowest MAP. Once that's dialed in, sweep the timing from your initial through your total in increments and adjust idle timing for lowest MAP. Since the car is an auto, I like to do this with the car in gear, because the load will change as the converter acts on the engine in gear.