I have been in 60 degree water with a 2 pc 3 mil and have been comfy. On the other hand, I have been in 70 degree water with a 3 mil and have been cold. Everyone's body metabolism is different, so what might be good for me may not be good for you.
I believe it also depends on your activity at depth. If you are "moving" then the 3 mil might be ok, but if you are sitting on the bottom waiting your turn to do a skills test then it might get chilly.
I have also seen people dive off Catalina in 55 degree with a 3 mil, no gloves, no hood. Incredible!!.
A hood and gloves are definitely recommended, IMHO, to help keep the heat in your body.