I rewatched IV. Kirk and co. take the Bird of Prey to Earth from Vulcan. Not long after launch (I suppose), Sulu announces: >SULU: Estimating Planet Earth, one point six hours present speed. That's 96min. I seem to remember reading Vulcan was supposed to orbit the real star Epsilon Eridani -- that's 10.5 l.y. by the classic rule speed = (warp factor)³ x speed of light, that's warp 38.6. Isn't that too much? (still less that JJ's warp) However, Scotty said he replaced the Klingon foodpacks. So they were planning to eat during the flight. That may indicate the voyage was intended to be much longer than 2 hours. OTOH, maybe a ship may be required to carry food on all flights.