Heat Range Experts: What plug to use?

I know the 'manual' lists a N13Y for the 8.6 360 and a N9Y for the 10.5 340. When we machine and rebuild these engines, what plug range should I use? I have a 9.5 340 and a 9.4 360. My 360 is missing occasionally and I am running the N9Y Champions. I think they are too cold a range for the 9.4 compression. I am using a Bosch Platinum plug in my 340 and it runs fine. It is the same "range" as the N9Y. What plug should I put in my new 360. I have about 150 miles on it and will start to work it a bit, soon. I am wondering if a N10Y would warm it up a little and stop the fouling. N12Y? What do you guys run on these street motors?

I'm running N12Y Champion in my 340.They work fine for me never had any problems with them.

See if you can find some RN11YC's but do not use a bosch platinum, these are junk in a Mopar. I have removed too many sets for customer that came in with misfires.

EvilScamp: What is your 340's compression ratio with the N12Y? I am thinking that a set of those will work in my 9.4 360.

SixPack: What about the RN11YC plug in the 340? What compression ratio are you putting these plugs into. Maybe I should try that in my 9.5 340 instead of the Bosch Platinum plugs.

I know the heat range was 10 for most of theMopar muscle cars that were over 10:1 compression.
RN11YC were used in the mitsu 3.0L engine that had 150-160 psi cylinder pressure so I would think they would probably work well for your application.