Performance drop off

[Dum-Dum]

adding a few 10s of psi down the inlet isn't going to increase peak cylinder pressures significantly over what they are already, ie stupidly high.

Doesn't work like that, 10psi boost dosen't add 10psi to the peak cylinder pressure, its 10psi multiplied by the compression ratio (23:1) ish so you actually add about 250psi to the pre combustion peak pressure.

You tend to lose around 1.5% peak bhp and torque for every 5*c of extra inlet temp.

The factor the Amerians always talk about is 10% for every 100*F. Suppose its about the same difference really.
However 10% power loss on a 170bhp DTurbo is almost 20bhp