I don't think you will find a 'perfect' answer on this. I'm running an electronic ignition on my stock 250 and am still running into pinging on uphill loads. I've got mine set at 8.
Trial and error is what I've been doing and what has been suggested to me. Too much advance and no pinging and no power.. too little and you have the power, but also the pinging. Other here know more, but this is what I have run into.
