I have been reading up on ignition timing quite a bit. I'm no expert, so here's my understanding. Please correct me if I'm wrong, because I want to do it right!To an extent, all engines will have an increase in idle rpm with an advance in timing, but that won't be an indicator of correct tune.
From what I understand, the best timing at any given RPM (assuming no knock) is the one that gives the most torque. I saw a video that gave a rough graph of torque vs timing. When well retarded from optimal, the graph is pretty steep and each degree adds a lot of torque. As you approach optimal, the graph levels off and then starts to drop when you pass optimal.
I'm not on a dyno yet, so "highest torque" at idle is highest RPM for a given idle setting. Same tuning process as setting idle mixture. One could also say, highest vacuum at a given idle RPM.
It will be next to impossible to tune partial and full throttle openings below 2-2.5k without lugging the engine, so I'm planning to revert to stock timing once the throttle cracked, up until 2-2.5k. Hopefully it won't make the throttle response weird.