There are some very deep features on that part with radii that are too small to permit milling tools to 'make any time'. If all the internal (deep) features had a radius of .385", one could then probably do it with a 3/4" ballnose tool: just set up the toolpath and let the machine run. A 3/4" diameter tool is about the minimum that will work 3" deep without pulling a miracle out of.......the thin air
Whenever you add unequal radii at the bottom corners of a deep pocket, it just makes finishing more of a pain unless the design is such that a large diameter tool with a small radius tip can do the job, for example a 3/4" bull endmill with .1875" radius corners. I've not seen many designers that actually know what the tools look like and how to design to use the features of the tools.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)