I have had a 550b since 1995. It is as close to fool proof as it gets. One thing I would caution about it, get the roller handle, that gear shift knob will put blisters in your palm. I have 2 RCBS presses and the 550, and it doesnt get any better.
Get a tool head for each set of dies, get them set and if you want to change out, simply pull the pin pull out one caliber and set it on the stand and slide in the next one, replace the pin and go.
On .45 ACP or .45 Colt, you can easily do 400 per hour if there is no distractions. You need your loading bench where you can lock your door and have no distractions until you are finished. I am a firm believer in locked doors to avoid distraction ever since my failure to lock a door allowed a person to come in behind me and slap me on the back when I was making a cut on the table saw and I shoved my hand through the blade and cut off the end of my left index finger. Basic safety begins with concentration on what you are doing and no possibility of anyone distracting you. Of the thousands of loads I have done on the 550 I have not had a squib or a double load. If you have the 650, you already know about full stroking the handle.
A picture of my bench is on the last page of the lets see your bench thread up above.