> maximum final Delta V from source of circa 58,000 ft/sec
Einstein would like to have a word with you. That word is "relative". Suppose there is a planet traveling away from the earth at at 50,000 ft/sec. An alien on that planet can fire a rocket, which can travel away from that planet at 50,000 ft/s, meaning 100,000 ft/s relative to earth. As it catches up to another planet, it might photograph some other aliens launching their own rocket at 50,000 ft/s, which is 150,000 ft/s relative to earth.
In fact, the SAME rocket could from earth to the first planet, then be launched from that planet, then stop at the next planet and be launched at 50,000.
Come to think of it, stopping at each planet doesn't change anything. It's ALWAYS standing still relative to something, and can launch away from that something to 50,000 ft/s. The gas leaves nozzle at 58,000 RELATIVE TO THE COMBUSTION CHAMBER. In other words, it can always go 58,000 faster, as long as it can fire it's engine. 58,000 is the limit for a BALLISTIC projectile, one that is fired from a gun and doesn't carry a working engine with which to keep accelerating. The limit is 58,000 RELATIVE TO the chamber in which the gas is burned. By carrying the combustion chamber within the craft, it can accelerate until it approaches C.