The II-A, II and III-A will all probably "stop" most calibers up to the 44 magnum. There are various youtube videos which tests this assertion. However, the problem is the force behind the round. Even though there may not be a penetration, the force behind the round is enough to create a lot of pain and internal injury. So if you are wearing a II-A and get hit by the 44 Magnum there may not be any penetration, but its going to be like someone just hit you with a bat accompanied by a lot of pain.
If you are keeping a vest by the nightstand "just in case" it will probably be useless when the time comes because of the amount of time to put it on and adjust it. Your best bet is a front-opening vest like the older version of the Point Blank Interceptor or the Point Blank NATO. The vest you put on like a jacket is far superior in such cases where you need to throw something on quickly. However, that type of vest would not offer the greatest amount of protection as you want the openings on the side rather then the front where rounds are most likely to impact.
I highly suggest training extensively with any body armor as it takes a while to get used to it. You might find the extra pounds slows you down or distracts you away from proper aim. Most people who aim and shoot at something miss the target. So if you are moving quicker you become a bad target. If you are slowed down by some armor then you will be a better target.
Someone had stated "why not just go naked?". Well, in actual combat, the US Navy Seals in Vietnam did everything they could to lighten their load to include wearing light tennis shoes and no helmet in certain operations. There is some value to going into a situation light rather then loaded down with gear. There has been test after test which shows the greater poundage over 35 lbs for males the less effective you become.