Plug change. Heat range too hot?

[67428GT500]

I have been running FR4 plugs with the Edelbrocks heads. The Edelbrock recommended plug is a Champion RC12YC.  I have never had a Champion plug I liked and I saw many of them being returned due to failure in vehicles.  Two plugs were recommended here. One is the NGK FR4, the other BKR6E.  Remember, this is a factory dual quad car that is street driven with the occasional "blast".  There is some soot on the body, which I am a bit rich but much I see a lot of gray on the electrode and ground. I had a set of BKR6E in my cabinet. Any reason not to run them?
Is there another recommendation?  I might add that I am also running the Pertronix II and matching coil. Direct 12V power source to the module as instructed. The compression ratio is about 9.8:1.
Any suggestions would be welcome.

[My427stang]

I have run the Champions and 3924 Autolites, almost every one ends up with the Autolites because you can get them anywhere and cheap, both work fine on the street though. I will throw a set of the race version 3924R in now and then, but I don't see any real benefit when I do. 

I see no reason your NGK won't work just as well

[cammerfe]

Back in the day, running the Thunderbolt, we were given plugs by the case. We quickly found that it was necessary to change Champs after every run,

A switch to a case of Autolite resulted in being able to run a set of plugs all day. We'd change them Saturday night in preparation for Sunday. The only drawback to the Autolites was that in order to get a new case of plugs, we had to bust the porcelain out and return the steel shells. We rigged up a holder in a HD shop vise and just gave them a lick to punch the core out. I can still see the burn marks on my arms from changing Champ plugs on a hot engine between rounds.

KS

[67428GT500]

I can't even imagine doing that on an FE mustang with power brakes between rounds. With the factory Cobra -Le Mans cast pent roof covers you're lucky to get the plug wires back on correctly.