Not sure how helpful this is, but I have used 15x and 16x binocs for the past 11+ months, on a near weekly basis. Sometimes daily. Both are image stabilized though, so I can't comment on the shakes.
Given enough practice, you can get on targets surprisingly fast freehand. With time, the human brain adapts. But it may not be in a handful of sessions. But keep in mind that mine are stabilized.
As much as I love my 8x42 binocs, I will usually grab the 15x50 for just for walking/hiking and checking things out, or casual glassing from a vehicle. When actually hunting I use the 8x42. Even stationary, the 8x42 goes on a tripod looking for movement as the FOV is more important to me than the magnification.
The biggest downside to using a 15x/16x to me is DOF. That higher magnification has less DOF compared to an 8x or 10x. No way to get around it simply due to the magnification, so you'll be focusing a lot if scanning close.
I think that a 10x50 is a great idea. I really don't need more binocs, but if I bought another 10x it would be 50mm.
Good luck and please let us know what you decide!