Modded 360: Not sure of Sparkplug Heat Range

Ok guys and gals! My 360 is beefed up some with 340 X-heads, 292 mopar purple cam ( advanced 4°). KB107 flat top pistons not of actual compression, Victor 340 intake. 727 trans with an FTI 9.5" 3400-3600 stall converter. 3.91's out back. So my old set up was a 280 mopar cam and 3.55s then. That set I ran rn12yc plugs and did good. With this new set up do I go one step colder (rn11yc's)? Or stick with the rn12's? Please fill me in!