Ive used a fixed temp 50W Weller for 30 years with no problem. Unless youre a plumber that's more than enough soldering power. I have a 2mm tip and it has enough heat to solder stainless steel plate, brass plate, piano wire, etc. People that say you need more than 50W heat don't know how to solder. The secret to good soldering is to make sure the parts to be soldered are super clean. The solder should flow over the parts like melted butter. If it doesn't then the parts you are trying to solder have an oxide layer on them. No amount of heat will remove this oxide layer and the solder will ball up and not stick.
The best solder flux I have come across bar none is phosphoric acid. It will not attack metallic parts. Clean parts well, apply phosphoric acid, if it starts to bubble there is still a layer of oxide on the surface you are wanting to solder. Once the bubbling stops, surface is only metallic. Wet the soldering iron tip with the solder. Apply iron to surface and simultaneously apply solder to the bridge that has formed between the soldering iron and the initial solder that was on the tip. Solder should wet the surface immediately and flow like melted butter. Move iron along the part and feed in solder.