I'm not familiar with your engines so its hard to be certain, but your running lower content nitro so I would start with a McCoy 59 (hot) or simular to start. If you were running 30% nitro in two different brands of highend, high-strung race mills it may be different.
If possible check with the manufacturers to see what plug they recommend. They'll most likely recommend their own brand of course, but you can get a temp range and go from there.
One other thing is to make sure neither uses a OS style short plug. Again check manufacturer. Hope that helps