I frequently read that the best time to hit The Race is at slack.
So if Eldridge lists flood current starting at (for example) 4:44 a.m., max flood at 2 hours and 45 minutes after flood starts (so, 7:30 a.m.), and ebb starting at 10:40 a.m., does that mean that slack is from 7:30 a.m. to 10:40 a.m.? Of course all of these times are approximate in real life.
Jon is correct, the period of actual slack is rather brief and odds are it will not happen at the exact time in Eldridge. All things considered, Eldridge is very accurate but not perfect.
Power boaters may prefer slack because they are less concerned about current than sailors and slack is less choppy.
Like most sailors, you probably sail as much as you can before turning on the engine. That means that you might end up traveling at 4 knots or 7 knots, depending on the wind. You need to give yourself at least an hour before slack because if you are late you will hit the flood and be sailing backwards
To answer your question more, it really depends on what direction you are headed and the weather.
You may want to transit the race and the sounds with the current. The more current you have the faster you will sail.
If you have strong headwinds and a destination to get to then you may want to motor. In this case you want to be closer to slack but still have the current with you. This reduces the amount of current against the wind. At max ebb/flood it can get pretty harsh under these conditions.
If you are exiting LIS and heading back East then you want to try and time the race close to the end of the ebb tide. This will allow you to ride the tide out of the sound and through the race. As the flood begins you will ride that back East.
Coming from or headed back to Noank, I always plan on hitting the Race, the Gut, Watch Hill, Wiccopesset, etc. at Max current (unless I'm headed towards Shelter Island or coming from that direction). This gives me a couple hours to spare one way or the other.
The bonus is; if it's a nice day and you are making hull speed you break the sound barrier if you have max current with you. You won't hear the sonic boom, but they will.