Spark plug heat range.

I have a 440 with about 11.5 to 1 compression. The cranking pressure is 210 psi. I've been running it for over a year with Champion RC12YC plugs with no problems at all. I run 93 pump gas with Klotz KL628 octane booster and I'm not getting any pinging or dieseling when I shut it off and have not had any plugs foul at all. In fact I have had the same plugs in it since I first got it running. A fellow racer is insisting that I should go to a colder plug because of the compression ratio. Just wondering what anyone else's thought are on this. Seems to me that if its not pinging or fouling plugs I should not need colder plugs. Also I should mention it has 440 Source Stealth aluminum heads. Thanks in advance.