Couple of thoughts.
0. The target output voltage may range from the mid 13's to the mid 14's, and not for reasons that are immediately obvious. That depends on the vehicle and the installation. It's also possible the target alternator output voltage will be pretty constant at around 13.7-ish volts. I've thought about this a couple times when people are talking about replacing their TV or trailer batteries with a different chemistry ... I haven't looked into possible side effects (and maybe there are none), but it's something I'd write my own FMEA for if I was thinking about doing it.
1. The pulley ratio comes into play. Quite often the alternator will be spinning 2 to 3.5x as fast as the engine.
2. Alternator power output varies not only with speed but with temperature. An alternator rated at 150A at 3000 (alternator) RPM, may meet that rating at an underhood temperature (technically alternator temperature) in the 20-40C range. At 50 or 60C, it may be 10-15% less, and it may be capable of producing around 170A at -30C. I'm attampting to past a link to a pretty crude chart of output vs temperature vs alternator RPM. If you pay enough money or are getting paid to write or use them, there are similar graphs with 3-5 temperatures and a similar number of speeds. I did a quick look on the web and this was reasonably close to what you'd get.