The 223 is a three stage pump, which may appear at first look to be a 4. First and second stages are together in the larger cylinder assembly. The third stage piston is small, and sits on top of a larger diameter guide piston. The cylinder is of two diameters to accommodate the two joined pistons, which may make it appear to be two stages in that cylinder assembly at first glance.
Not sure what to say about the pressure question. I have a little experience with a 223, but haven't run one for long periods to see how much heat they generate. Rumor has it that they run pretty hot, and I/R has even suggested in writing that their breathing air compressors should be allowed cool down periods instead of running continuously for long periods. I will try to find that bulletin and post it if I can, but it was a long time ago.
Anyway higher pressures equal hotter temperatures, which can lead to faster wear or oil ignition in extreme cases. One way to help compensate is to slow the rpms down a little with a smaller drive sheave (or an adjustable one... my preference). Of course you lose some cfm doing that. Not saying that higher pressures can't be done, but with the manufacturer having reservations about heat build up I suggest caution. I will try to find out more. Sometimes I am overly cautious about these matters!
Also could have been a later version, resulting in a 4 stage, but that typically would include a change in model number, and I have never heard of one.
The older I get the better I was.