In a perfect world I would have a turbo p-port 3-rotor. :-)
I sort of ended up with a turbo because it was just sitting there (came with my '91 turbo engine) so I decided to try it on for size and it never went away. I am glad I have it, but the 3-rotor and/or p-port would have been nice options. The turbo quiets things down just enough to be tolerable, but my formation friends can hear me when I am flying on their wing... largely because the sound is different, but it is also a little louder I think. But is is quieter than a n/a rotary engine by just enough to matter.
The turbo is not particularly less expensive than a p-port in the long run. By the time I got most of the issues worked out I am in for over $5k in turbo rebuilds and non-fitting manifolds etc. Even when cared for correctly (keeping EGT down), they are only going to last 1000 hrs or so (who knows) and each rebuild costs $1k. In the long run though, these costs or the costs of a p-port or 3-rotor are trivial when compared with the cost of operating an aircraft. If my turbo has cost me $5/hr, then Avionics have cost $20/hr, gas has been $45/hr and the hangar has been about $50/hr. Dont let the relatively small cost differences sway your decision here.
The turbo definitely adds much more power than p-port would, both down low and up high. And with the p-port the sound issue is not trivial if your are going to be maximizing the power output. Lets put it this way, you wont find me ever removing my turbo.
But, if I were to do it again, I would probably go with a 3-rotor. Pretty close to the same power as the turbo, weighs a little more but is more reliable and efficient. There have been many examples of successfully (and continued) flying of turbos and 3-rotors. But p-ports in aircraft are sort of like UFOs: you hear a lot about them, but you never really see one.
Not to say that p-port isn't the best option. It is light weight, simple (in a sense), reliable, efficient, lower drag, and brings the power of a 2-rotor right where you need it for something like an RV.
I hope this discussion has be helpful (yea right!).
Dave Leonard