What will you be shooting....?
IF you don't need the high speed flash sync I would stay away from the Schneiders.
The Mamiya 2.8D is a brilliant lens. One of the very best medium format lenses in production.
Not only is it sharp, it also has very nice bokeh and immediate focus fall off is very nice too.
The only thing that may be a problem for you is the vignetting the 150mm 2.8 has when shooting wide open.
While it is smooth and actually quite pleasant due to it being combined with the nicest bokeh on a modern 645 MFD
it could be an issue for technical photography.
It can be corrected in post, but it is a 1 stop correction so corners are "pushed" one stop.
One other important thing to consider though regarding leaf shutter or focal plane shutter is actual overall shutter release time.
While a focal plane shutter has higher top speeds the actual duration of the whole exposure is 1/125th of a second.
The shutter sort of scans over the sensor exposing a slice.At 1/4000s each pixel gets a total of 1/4000s, but they are not exposed at the same time.
This can lead to distortion with fast moving objects.
With a leaf shutter set at 1/1600s the whole exposure takes part in that 1/1600th of a second. All the pixels are exposed art the very same time.
Here is a high speed video of a focal plane shutter. You can see that the shutter at 1/1000th never fully opens, but opens a crack that then scans
over the sensor.http://www.youtube.com/watch?v=-isRz54C_vY
Now going back to sharpness camera shake is not your only problem. A kenyon gyro will help a lot, but the chopper's rotor blast will be your main issue.
Both the low frequency noise and percussive impact of the wind will "eat" sharpness.
That is why the best results are obtained shooting from under a chopper or out of a "hole in the floor".
If you are going to do a lot of helicopter photography I would strongly recommend putting the budget towards a Nikon D800 and running it remotely in a pod system
that you can mount under the chopper. You can remote the camera with either Nikon software or Control my Nikon.http://skyimd.com/skydslr.html
You sit safely and comfortably (well as comfortable as a chopper can be). You use real time live view. You can use VR stabalized lenses for shooting at dusk and sunset.
D800 vs IQ180:http://www.circleofconfusion.ie/d800e-vs-phase-one-iq180/
I have also seen some amazing work shot with a pod on a small airship all remotely controlled.
Going back to the Kenyon Gyro and results with a camera.
With a Kenyon of whatever sized one you will get you will get far better results with a light camera.
That is another reason why I recommend a light D800 rather than a much heavier MFD.
Put a bigger kenyon on a lighter camera and you will fight vibration and prop percusion much better.
My cousin is a geological arial photographer. He now gets better results with his D800e plus gyro in a diy pod that he was getting
with systems 20 times the price. What's best is he flies with two systems.
Oh one other tip. Keep in mind that you do not want to have your gyros spinning with the rig receiving mechanical vibration
from the helicopter frame. It will kill the gyro in no time.