Cargo Pod for P models?
 

Does any one know if Pressurized Skymasters can have cargo pod installed? If so, what's the cost in speed to a P model?

They Can.

I have heard the speed penalty is around 3 or 4 knots.

I heard that as well, that it was a 3-4 mph (or Kt) speed penalty.
Then I put mine on, and flew south. I put several hours on it. Mostly in hot humid weather. I noticed that it actually took about 10 mph off.
It may have been other factors, but there was a significant speed penalty

I can't speak to the P models but on my normally aspirated model it was well within 3-4 knot range. It is literally the best money I have spent on this plane (altho I'd like to say again what a HUGE pain it is to keep clean of exhaust).

I was heavy, all the time I had mine on, so I'm sure that was a factor.

Oh, and I have a normally aspirated model as well.