definitely do not let te car leave your sight until the check is cleared and it has been confirmed that it is cleared. DO not be afraid of the sale falling through, but rather of being scammed. Most of the "nigerian" scams work this way.
they send you a check for X amount let's say $5000. Then they tell you to keep $1500 for your efforts (or some sort of research, or whatever other task they come up with), and the buy a MONEY ORDER or get a CASHIERS check from your bank and send it to some other person. Now, you do this, and several days later you realize that their check has bounced, and that you send out actual "cash" to the other person. So, you find yourself owing that money to the bank.
Bottom line - if he is legit - 3-5 business days is not too long to wait for the check to clear. Especially when taking into consideration amount of $$$$ in question, as well as the distance that the car will be transferred.