I have both. In fact, I have two Stingers; one purchased six years ago, and one issued to me last year.
The older one has a new battery stick, but it is definitely not as bright as the newer one, right off the charger. Must be a different bulb...
My 6P is 6-7 years old as well; and I think it is a bit brighter than the newer Stinger. But I wouldn't want to live on the difference.
You're talking about two differnt concepts here. The Stinger is a good all-around genral purpose light that can be recharged; i.e., it is not expensive to operate. It is too big to stick in your pocket for casual carry.
The 6P is what I would term an "emergency light"; small enough to be there when you need it with the power you need, but expensive to operate. Recent discussions regarding bulb life have me wondering; this 6P has seen quite a bit of use, but it is just as bright today as it was when I bought it.
Anyway, keep in mind that the Stinger is basically twice as big as the 6P. If you're looking for something to carry, that is a factor.
But for all practical purposes, the ones I have are equal in the light output department.
Steve