Let's back up a second to ponder what this test actually shows. It is showing that two different irons require slightly different *set* temperatures to attain an equilibrium temperature on the double sided heat sink of approximately 200C. Nothing less, and nothing more.
This could of course just be a simple calibration issue as each tip temperature. Contrary to KL27x's assertion, the actual calibration of each station matters because the energy delivery is directly a function of the temperature delta. The hotter tip temp (actual temp, not displayed point) holds more heat (thermal mass). But more importantly, it determines the forcible power delivered to the heating element by the controller logic. Basic PID thinking shows that you can't get a 60w station or iron to use all 60w to recover from just a 10 or 20 degree temperature drop.
Incidentally, this flaw of relying on set temperature was present in Dave's testing also.
What I have learned from a lot of testing is this: at low temperature setpoints, the station itself matters almost zero because there isn't enough temperature difference to place much load on the station at all. In Dave's testing, the 240C set point is probably < 10w of actual forcible power dissipation.
You can't prove a powerlifter is stronger than me just asking us both to lift 10kg. If we're both capable, it only proves we're both sufficient and says nothing of our relative capacity.
So a long as we are operating with thermal loads well below the ultimate capacity of two test specimens, the station power doesn't matter even a little.
So what does matter?
The single most important element of thermal performance is the plating thickness of the tip. A more durable tip with thicker iron over copper has worse thermal performance. This is significant enough that JBC actually makes two different series of tip, one is "high performance" (i.e. thin plating) and the other is "enhanced durability" (i.e. thicker plating). Hakko is well-known to favor durability and has rather thick plating and thus less thermal performance than knock-off T12/T15 tips might have.
Copper is 4.5x-7x more thermally conductive than iron (386w/m*K vs 55-80). The thickness of that plating and that amount of reduced conductivity is VERY significant.
The plating thickness actually matters more than the overall heat capacity of the tip itself because it determines how quickly heat can flow out. A thicker plating not only lasts longer but creates the illusion of more heat capacity because it slows the heat flow out. It like the illusion of having a larger gas tank just because you limit the throttle to 50%.
If plating thicknesses are the same, then the overall heat capacity of the tip matters next.
Notice, we haven't yet gotten to whether the tip is cartridge, RF or slip-over-ceramic-heater because up to this point, it doesn't matter. Until and unless you are draining the thermal reservoir that is the tip (through the restriction of its plating) then the ability to replenish the reservoir doesn't matter. You'll always have enough "water."
There differences in pure thermal performance between most irons can be offset by just setting the poorer performer slightly hotter to get about the same forcible thermal dissipation. They are meaningless. SO the hakko needs to be at 330C to perform like the JBC at 310C. Does that matter? Not in my world.
Which means the appeal of a T12 has almost nothing to do with "superior" thermal performance. Rather, it's a smaller, lighter handpiece that's shorter and easier to use and that doesn't get nearly as hot as the ceramic element heaters (like the 888) will get in your hand.
I'll be getting an FX-601 soon enough. I can guarantee you that even at only 65w, I will be able to show that the T19 tips "outperform" an 80w 888 with T18s under some conditions. More mass, more capacity, same plating thickness. I'll be buying it just for that 6.5mm chisel that has no counterpart in the T12/T15 range.