The hole is to clear the vapcap and allow air into the vapour mix.1) I can confirm the relevance of the hole. Is it just me?
There's two bi metal discs in the cap rather than relying on just one. Usually there's two clicks that come from the cap on heating and cooling.2) Why do we call it click when it is actually more some kind of "click-clock"?
The ergonomics of the XL size stems work better for my big hands, though I could see someone with smaller hands liking the regular size.3) I'm now kind of sure that the XL is worth it. I think that even slightly longer would not hurt!
Low density and low mass makes for quick heating and cooling.4) I don't know for SS, but Titanium hets and cools incredibly fast. Amazed.
The hotter and wider the heat source is, the shorter the time it takes the cap to click, and the tip will be proportionately cooler. Wider flames are less precise with the heating and offer more of a general ball park for temperature because they bathe the whole cap in flame.5) A three torch lighter is nice, but I wonder how a 4 is. I just don't like waiting for two long 'cos I hate the noise of the lighter when it's on.
The smaller and more focused the heat source is the longer it will take to click, and the tip will be proportionately hotter. Smaller single flame torches are more precise with the heat placement and allow you to fine tune the temperature when it clicks.