recommended wattage for soldering station
At work, I have been using a solder station from Weller. It had a 80W iron, which was still very handy: Not longer that 18cm, a not too thick handle, and the heater was as thick as a pencil. The tip was exchangable, we had fine, needle-like tips for soldering SMDs as well as more bold ones for thicker cables like 2.5mm² and more.

Sometimes, I also soldered more heavy things like ground straps with it, but this isn't fun. The iron had not enough power, and due to it's size, also not enough heat capacity. I had to set the iron to 480°C and wait a moment before I could solder. The result was... well, there was an electrical connection, but I wouldn't call it reliable.

It is clear that this temperature is far to high, the flux just burned, the tin had a bad consistency, the tip didn't like it, and you can apply too much heat.

We also once had do solder lots of thick cables like 16mm², therefore we got a very strong solder iron, I guess a minimum of 150W.

So, my personal conclusion is that a regulated solder station  in the range of 60-100W with exchangeable tips of different size is fine for standard jobs from small SMD soldering up to standard mains cables. For that 16mm², you should have an extra iron, I recommend at least 150W, or more. (Also, that 16mm² stuff is usually not that sensitive to over-temperature.)