I highly prioritize fuel efficiency. Heck, my newest generation of fighters can go nearly 10 billion km (up from 8 last generation).
Also, due to the quirks of my galaxy layout, it's at least a 10 billion km trip from Sol (where my shipyards are) to anywhere else. I want to move the 'yards somewhere more centrally located, but the crazy manpower requirements have stalled progress on that front until I can build up population in the colonies.
My explorer ships have deployment times of 3 years, and maintenance stores to match - they're as fire-and-forget as I can make them. Admittedly, 810 billion range is probably more than I need (they usually time out or start running low on supplies first); but they're only running with 750,000-size fuel tanks - the efficiency of 5,000 ton engines with 30% fuel efficiency and 50% power stack to a crazy degree.