Something else to consider it the distributor used. As you increase the gap of the plugs it will create more KV at the electrode. Make sure the distributor cap is clean and doesn't have alot of the conductive dust. Perhaps more chance of ionization if you go higher in plug gap.
This is one of the benefits of having a Mallory Unilite or MSD distributor.
Another consideration that must be noted is the coil. If your using a bosch blue coil it should have enought reserve with the coil winding ratio. Using a Blaster 2, Blaster SS or Blaster HVC will easily provide enought KV since its designed to work with a Capacitive discharge box.
With my pumpgas 2332 which has had a combination of 9.5:1 c/r and 10:1 c/r I've used .045 plug gap. The gaps are something I really haven't played with but currently whatever the gap is it runs