spark plug heat range

i run 111 race fuel in my car at the track and pump on the street after i turn the timing down and i run auto lite 64 would like to try a colder plug i had 65 and changed at the track to 64 dont know if the car just like the plug or i just did something diff. but it did go a hair faster but i was testing the new motor and learning myself....by the way is that the comp cam 282xs...if so how fast have you been with it...thats whats in my car and ive been a 7.54 with a bad 1.67 60' made a few changes and hope for some drop in et..