This thread does interest me. As mentioned the R380 was named due to it being able to take 380nm torque (280ft/lb) but anyone who builds anything for mass production puts in redundancy, according to my engineer friend there is usually at minimum a 50% redundancy. So in theory that gives 570nm (420/ft/lb) before failure.
Plus on top of that there is the likes of TD5Inside (new Td5 is pushing 250bhp (tis a 2.8) and bundles of torque), Gigglepin (in the past) and a few other companies who use R380 boxes with a hell of a lot more power running through them than standard. Suppose the questions is longevity, but as mentioned as long as you stay sensible and dont try to get wheelspin etc... likely hood is the box will be fine. Also according to Giggle pin the Transferbox can take upward for 500bhp, again though longevity....
From what I have read and researched a re-map and larger intercooler with a boost tweak won't harm any of the transmission elements, unless you really push it hard. Mine has been mapped, larger intercooler, boost at 18psi, been that way for a year 5k miles, not had any issues as far as I can tell relating to the upgrades bar the clutch release bearing/spigot bush failing but there is no reason to assume they are related. To be honest I could not imagine going back to a standard Fender after building mine up to what it is.
As for the smoke issues, pre re-map (dynachip) I had zero smoke, ran very clean. After the map I did get a puff of black smoke upon changing gear however this went as soon as I fitted a larger intercooler. Since then runs as it did before just greatly improved.