Might be worth putting a wattmeter on an oversized BEC and work those servos hard. Add a safety margin to figure out your BEC. Like you, I prefer an oversized BEC on my bigger aircraft....wait, the 08? The 8g servo? What in blazes are you flying that is small enough to run on 3x 8g servos yet consumes 65amps! That's a BEAST!
Anyhow, 4amps should be good for 3x of those servos, but I can't find any specs that define the stall current (frankly, it seems no servo producer is willing to give that number anymore). If you don't have a way to hook up the wattmeter directly to the servo, then just connect it to the battery. If it is accurate enough, you should be able to measure the current with no servos, then plug in a servo to get the idle current, then apply resistance to the servo arm and give it some control to measure the stall current. Don't do this for too long, as digital servos will apply full power to get to their destination, so you could eventually burn out the motor. 2 or 3 seconds should be plenty.