Exhaust and air intake temperatures

On a Petrol turbocharged engine EG Audi 1.8T what sort on Maximum exhaust gas and air intake temperatures are we looking for for reliability?

There are very few absolutes here unfortunately and maximum EGT is not always a defining aspect of engine reliability since it's affected dramatically by ignition timing as well as AFR. What I can say is that for the most part you'll find turbine wheels tend to start showing signs of heat related damage if they consistently see temperatures above about 1000 deg C and I'd normally expect to see maximum EGT between about 900-1050.

As for IAT, less is always better. There isn't specifically a maximum temperature above which you risk damage, however as the IAT increases you'll make less power and you may find the engine becomes more prone to knock. I like to see IAT within about 15-20 deg C of ambient where possible.