Hmm, so what I'm getting from this, is that the actual generation parameters from the temperature map (the ones I turn off in PW when the temperature map is selected on the parameter tab) are not subject to the same limitations that the pre-set map data is. ...
That's my understanding, yes. I don't know if it's intentional or a bug, but that's exactly the behavior.
We can't set the temps outside a limited/capped range (that specifically is
NOT lethal), even if you use a pre-set-values map. However, if you use poles and set the temperature high enough or low enough and let the old (pre 0.40.9) pole behavior produce the gradient, you can get lethal temperatures.
Short version; with poles = potentially lethal temperatures. without poles = ~always "friendly" temperatures.
Another interesting behavior I noticed when testing this... if your temperature is high enough or low enough, on the embark finder, you'll get the "NO TRADE" warning come up. In the past, that would prevent trade caravans from visiting. Currently (at least, in 0.40.12) this is no longer true, and Dwarven Caravans visit (and suffer cold damage, at least) regardless of this setting.
This has the consequence of causing potentially tremendous damage to containers, resulting in carried goods being.. "liberated" or destroyed from the caravan while they're on the surface.
Also, if the temperature is high enough or low enough, no animals of any kind will visit the embark surface. This, too, has some interesting possibilities for certain challenge forts. Even though animals will not visit normally, though, currently this doesn't stop the dwarven trade caravan.