The coldest plug will only be needed in a consistant WOT track situation. Find the series plug for your heads and if they are an Aluminum head, start with 2 steps colder than the recomended (from head manufacturer) plug. It is very easy to get TOO cold of a plug installed. If Iron heads, 1 step Colder. Keep an eye on them initially. This compression is not extreme by any means. Like it or not, 99% of your running is with the throttle plates "barely cracked"
