Hi, hcubell,
I have owned a P45+ on an H2 as well as a P45+ with a Phamiya AFD III for nature work (including wildlife/long tele work).
Shutter vibration in the "dead zone" 1/15s +/- a few stops is pretty bad for the AFD III, and every focal plane shutter system I have tried (Phamiya AFD III, Contax 645, Hasselblad 203FE). Each system was tested with 300 or 350mm lenses--given typical shooting times of day (ie dawn/dusk), I don't think the focal plane systems are really up to long lens work without extra gear (steadying arms, custom plates binding body to lenses, etc.) All of these solutions have their drawbacks, including additional weight, even slower working speed and inability to rotate from landscape to portrait.
I have used a Hasselblad central shutter 350mm as well as a Rollei 350mm central shutter and I can tell you the vibration is significantly less. Not zero, but manageable. For long tele work, I definitely recommend staying away from focal plane mechanical shutters.
As for the rest of it, the P45+ worked seamlessly with the H2. Aside from any shenanigans Hasselblad has played locking out certain lenses from being used with anything other than specific systems, my own opinion is that the Hasselblad system as a whole is more mature; much of the Phamiya's lens lineup is still awaiting an update to either the latest "D" or to leaf shutter glass. If you're like me, I assume you want to shoot now; I strongly recommend considering only what is available for general purchase *today* as you make your decision. Far too many promises are made and far too few dates are kept for my liking.
Leaning toward the H2. I don't see any specific advantages to the Mamiya--I did not care for the shutter lag issue, or the lack of compatibility with rechargeable batteries. Neither has a vertical grip available today, so they're both missing the boat equally there. I think the HTS, along with a shipping leaf shutter 300 combined with no real drawbacks (HCD issues aside) with the system would lead me in that direction, if I were in your shoes.
P45+ itself is killer--no worries on that front.
HTH,
-Brad