madness2007- the "hotter" the plug, ie. a p3/rt3 will have these characteristics.
- a broader tune window
-more crisp bottom end
-little more of a stable idle, especially if the LSN is a little rich
-usually used for break in period due to good idle and richer tune ability
-will not last as long as colder plug before having to be changed

a colder plug will usually
- narrow the tune window making the tune have to be more spot on
- increase top end performance slightly, smoother bottom and mid range
- be less prone to flaming out ( in my experience a 4 series plug or 97t has provided the best performance all around with greater dependability)

I would say for everything except extreme conditions a hot or medium plug will suffice. If the p7 is working for you great, but that is not a very popular plug among most for these engines.