Reading through this thread, I see lots of questions and few answers with a basis for them. There are some research papers out there that provide basic information and it isn't hard to do testing of your own.
Rotation (indexing). There is data on rock drill bit indexing. I know of a paper from the 1950's that quantified the amount of rock removed by a hit adjacent to an existing hit. They used a chisel bit and made parallel craters. They got an ideal spacing of something like 1/2 inch. I did some tests with rotational indexing of a 3/8" bit ground to a square chisel point and found that 45 degrees on a flat granite surface works very well. In actual practice, I think that drilling in a confined hole with a v-shaped tip is optimum at a smaller angle. Maybe 15 degrees between strikes.
There is also data for the rock volume removed in relation to the energy of the strike. The researcher varied the angle between the two faces of the drill tip and the energy of the strike. With a 60-degree tip angle, about 75 ft-lbs was optimum. I think this was a 1/2" bit. Energy is 1/2 mass times velocity squared. Solving 75 ft-lbs for a 16-ounce hammerhead arrives at a velocity of 69 ft per second or 47 mph. (somebody check my math). pretty slow compared to a 90 mph fastball.
All of the above will vary with the type of rock.
Sharper bits drill faster and bits with a smaller angle between the faces drill faster. But, too sharp and too acute results in tips that shatter or wear out quickly.
Howard Hartman, Basic Studies of Percussion Drilling, Mining Engineering Jan 1959
Howard Hartman, The Simulation of percussion Drilling in the Laboratory By Indexed-Blow Studies, Society of Petroleum Engineers Journal, Sept 1963
Kahraman Bilgin & Feridunoglu, Dominant rock properties affecting the penetration rate of
percussive drills, International Journal of Rock Mechanics & Mining Sciences 40 (2003)
Dingxiang Zou, Theory and Technology of Rock Excavation for Civil Engineering (Chap2 Rock Drilling) Springer, Nov 21, 2016
John Musselman, Rice University Thesis, May 1967
Terralog Technologies, Fundamental Research on Percussion Drilling (for DOE), Dec 2005