I just realized that I've been playing for a few years with a houserule that I can't find anyone else to be using (despite the fact that it's great!)
Speed Die - At the start of the Sea Movement Phase, have either player (or a third party; it doesn't matter) roll 1d6. Use the value of this roll for the "Slow," "Fast," and "Sprint" abilities of all units for both players. If a player has "Sprint" on one of his units, he must declare he is using the ability before the die is rolled.
This basically keeps silly things from happening with "slow" (such as a Royal Oak outrunning something like Nagato, or Tennessee and California not being able to stay in formation with one another) and takes less time to play out if there are many ships where "slow" is present on the board.