> I think it would be a pretty bad idea to use full acceleration for the entire trip inside the atmosphere. The huge speeds generated would either do damage to the ship, or (more likely) cause serious shock-wave effects on the outside <

Well, they wanted to get there as soon as possible. My guess is that max speed inside the atmosphere is going to be less than the 20 miles/sec or so the conversation implied. And Kirk was in a hurry. Best tactics depend on the characteristics of impulse. If, as has been implied, full impulse gets you to some max velocity more or less instantaneously, then the optimal strategy would be to blast straight up out of most of the atmosphere, go to full impulse until over the whaler, then blast straight down. If impulse more closely resembles newtonian acceleration, then the trajectory would be more of an arcing one, with top speed achieved while out of the sensible atmosphere.

Given that the survival of the race was at stake, and that the shock waves would be mostly over open water (and could be blamed on a meteoroid), i don't think Kirk would have limited his speed within the atmosphere due to worries about shock waves. Presumably this would reflect hard limits on what the ship could do. Still doesn't convey much useful information on impulse characteristics. Or why Kirk didn't just beam the whales on board as soon as he was within range, rather than confronting the whaler directly (maybe that was covered in the movie and i've forgotten. wouldn't have been as cool, though, and to Kirk image is important. And was there something special about these whales that required Kirk to risk changing the future by exposing himself to the whaler?).