answer...maybe
The book doesn't specifically mention exit strategy numbers for anything other than 6 and 8 decks. However, you could probably extrapolate from the 6 and 8 deck info. For a standard RC I would do this:
.................................................If RC <=...........
Leave.........................4-deck.........6-deck..........8-deck
After 1 deck dealt.............-12.............-22............-32
After 2 decks dealt............-7..............-17............-27
After 3 decks dealt............---.............-12............-22
After 4 decks dealt............---.............---............-17
I wouldn't bother remembering a number for after 3 decks dealt for 4 decks since you are going to be very near the shuffle point by then and you may as well wait for a new shuffle. Notice you add +5 to the RC for each deck dealt and you add +5 to the RC for each deck in play.
Only my opinion.