Right you don't really want to accelerate until you are loaded in the power zone to accelerate faster outward away from your body. It's basically just momentum bringing the disc into the power zone with you just guiding it along. Early speed means nothing if your mass is not behind it and makes it 100x harder to actually accelerate faster instead of decelerating. You want to be accelerating through the hit with all your mass leveraged behind it. Force=m*a.
So just using some rudimentary math concepts if only the mass of your arm is coupled with the acceleration, then your force to the disc=1200N=20lbs*60mph. Alternatively your force to the disc=10,000N =200lbs*50mph. So you are better off giving up 10mph arm speed to apply more force to the disc. This is where arm speed really means nothing until you already are using all your mass.
Regarding stride length, you aren't finishing balanced on the front leg - you are getting pulled off your front foot in the finish toward the left, you should finish more to the right of a braced front leg if your rear side comes through forward. A shorter more compact stride is much more efficient, quickly changing the acceleration and direction.
Most normal size hammer is fine or short handle sledge up to 3-5lbs. You should never be jerky with it, always smooth and relaxed yet deliberate with the head end. If you are going to actually release the head of the hammer with any kind of speed you better be outside and toss it, or actually hammer into something inside you don't care about.
