Dabbing into pour over, and I've always read if you don't have a thermometer, bring kettle to a boil and wait 30-40s before beginning the pour. However, when taking the temperature in the pot with a Thermapen, it was still at near boil temp at this point (I suspect at the rate I saw it decrease, would take at least 2-3 min to reach 205F). Is the 30-40s figure taking into account water temperature dropping as it exits the spout and hits room temp air? A sort of offset, similar to boiler vs brew group temp with espresso machines?

The Thermapen actually fits the stock steam holes of my Hario, so I'd prefer to stop it at temp versus bringing to boil and wait to decrease. I would just like to confirm if I need to remove the water when it reaches my desired temp (e.g., 200F), or wait until it's higher than my target?

Or is it also higher because you need to take into account the temperature will be dropping during the total time it takes to complete the pour over?

The variance in numbers probably reflects the variance in coffees and other techniques/recipes used. The slurry is often quite cool even with boiling water. Perger recommends boiling water but he uses super lightly roasted coffee.
Use your thermometer and experiment

Chris is right, lighter roasts taste good with water right off the boil, but more developed roasts may do better with a lower temperature. I've always found that dropping the temp a few degrees from the temps I brew my other coffees at brings out more sweetness with Ethiopian coffees.

I use a Behmor BraZen now and brew most Ethiopians at 198 (the BraZen is very temp stable and probably loses less temp from the kettle to the brew basket because it's almost a closed system) and other coffees up at 200 or higher F.

You can put the Thermapen in the coffee grounds to get a better handle on the actual brew temps and use taste to dial in your coffee from there.

I decant 208* water from my Zojirushi boiler into a proper pour over kettle. This helps lower the temp. If I were to use a kettle off the boil from the stove, I would decant it back and forth. Exposing the stream of water to the air will drop it quickly. FWIW, I like to begin pours with 203* water for pre-full city roasts. I drip slowly over 3 minutes when, by the end of the extraction, the water is more like 195*.

I use a Yukiwa M5 kettle

https://www.amazon.com/gp/product/B001U ... UTF8&psc=1

with the hole in the lid widened enough to accept a thermometer.:

https://www.amazon.com/gp/product/B00RP ... =UTF8&th=1

aecletec wrote:Perger recommends boiling water but he uses super lightly roasted coffee.
Use your thermometer and experiment

This. I think most recommendations to wait ~30s from boil are for lightly roasted coffees. Waiting 30 - 45s is sort of silly for most 0.5 - 0.7L kettles - the temperature maybe drops 2 - 3 degrees in that timeframe. I suppose this might be perceptible for some when pourover brewing, but I'd suggest there are other brewing variables that would have a greater impact than 3 degrees from boil.

I routinely brew darker roasts, so often use water at 185 - 195F with great results. I once brewed a batch of dark, caramelized French roast at 175F that was absolutely delicious. I used a Bonavita PID kettle for this - waiting from boil would have taken 20 minutes. The suggestion to decant back and forth is also a good one, if you don't have a PID kettle.

When using pourover devices,(kalita, hario, chemex, etc.) I set it to 205 degrees and hold it there while I grind my beans and then brew on a Bona Vita PID too. It is good to experiment, but 205 is my baseline when brewing a bean that's new to me.