Drop Fordem a PM, I know that he runs advanced timing on his.

The old folk here have a saying that goes like this - don't trouble trouble - in a nutshell, don't go making trouble for yourself.

From the questions you're asking it's clear that you lack the experience & understanding required, and probably the tools & equipment needed to correctly reset the timing at the end of the exercise - you're unlikely to be able to improve on the factory settings, so just leave it.

The ignition timing on most EFI engines (J20 included) is controlled by the ECU, and adjusted as necessary based on operating conditions, the adjustment on the cam position sensor is there to set what is known as the "base" timing - the reference that the computer uses to set the actual timing.

The engine seems to be set for around 20* BTDC - with the jumper in - and there is around a 5* variation (at idle) if the jumper is removed & reinserted. This is way more than the FSM specifies but is not that unusual here in Guyana, we get only one grade of gasolene - super unleaded - and it is common practice to advance the timing to take advantage of the power available.

I'm not sure if J20's are knock sensed or not. If they are, then increasing the base timing will achieve almost nothing - the ECU will already run the car with as much advance as possible. more base timing will only really effect idle and coast conditions.

Problem is, maximum brake torque (MBT) can occur before knock threshhold, so you can get more torque with a more retarded timing for a given load point.
I experienced this with my drover, i cranked up the timing and threw in some 95 octane, it "felt" faster on the street and it wasn't pinging. I jumped on the beech and it was really slow....and the poor engine was laboring. Got to the camp site wound the timing back a fraction, and it went 100% better.
On the other hand my old 4age, I advanced the timing a butt load and ran 98 octane, and it was definitely better.