You remember right, I'd agree that you don't want to be pushing Into 4 figures on any petrol turbo engine if you can help it.

Ref temps on diesels... It Varies from engine to engine and of course where you measure it. My personal limit for sustained hard use is 1250 Deg F post turbo and pre cat. The problem is, there are other mechanisms that are affected by heat and not just pistons and heads. Variable geometry turbo assemblies for one really don't like huge temps and tend to be far more reliable at sub 1000 Deg F. As always, everything's a compromise and one that a tuner has to choose. That graph you see above for mine is the max power this will do reliably while keeping temps at sub 1250. If I push them to 1400 I can see 375bhp and 600ftlb and that's with DPF etc still installed. Lots more torque is available no problem, it's limited to 550ftlb on purpose as that's a tad over the exceeded maximum torque figure quoted by ZF who make the box. The DPF and cats are a big problem when trying to exceed this power level on this engine as all these restrictions = back pressure and more heat. But taking them out means more power and more smoke. Not a compromise I can make on my own car. I love DPF equipped diesels, can't beat smoke free 45mpg motoring with power to back it up. Another 100+ftlb is available no bother at all but to be fair! it's not only pushing an expensive gearbox hard! it also makes it damn hard to drive without breaking traction! and as we all know, "Power is nothing without control". She puts 550ftlb without fuss at all times which is great for RWD... 600 makes it a lot trickier and therefore a bit slower in the real world where you no longer dare nail it out of a corner and know it will stay under control. That's where we lose with diesels, we can't have huge bhp with revs to do more work with less torque causing problems like we can with big turbo petrol engines so we have to maximise the limited rev range we have to best compliment the limitations of the rest of the chassis, which can be tricky with big torque numbers at very low revs with RWD.