Docter G,
You're welcome. I always like a good question when I see one. Hope I was able to make things a little clearer. Just since I am OCD I'll throw in a little more info.....
I wanted to point out that if your are concerned about detonation you will want to run the hotter plug within safe limits. A hotter plug will help prevent detonation in two ways: First, as I briefly explained earlier, the quicker burn will avoid detonation. Second due to a quicker burn the engine's timing can be retarded to make maximum power vs a hotter plug which would "want" advance to make peak power. Both of these factors lead to less heat before the piston reaches TDC (a good thing). Suffice to say that you want peak heat right after TDC and the hottest SAFE plug will be best for this. One last note is that a spark plug likes to run within a temperature range to avoid carbon deposits forming on the surfaces so going too cold can lead to misfires also.
You would need to run a hotter plug as you increase power since as we know the increased temperatures from high compression/boost/nitrous/toomuchtimingadvance can lead to the plug becoming so hot you have pre-ignition which is NOT detonation. Pre-ignition simply melts your piston away since you basically have a burn beginning WAY before the piston reaches TDC. Cylinder temperatures will spike to an insanely high level as the piston is trying to compress, and melty melt poof....game ovah. This is extremely rare btw...
That said, those are the extreme's so don't think you are going to do any damage if you are running a relatively safe tune, which is always #1 to avoid detonation (your timing sounds within reason btw).
I wouldn't worry about it much but if other's are getting away with 6's or 7's I say go for it!
Walker