Stealing some terms from wikipedia, it is due to the obliquity of the earth so that a more northerly latitude above the equator will always be further from the sun than a more southerly one. This increased distance accounts for lower average temperatures.
But I guess you weren't really asking that were you?
Chop is spot on concerning changes in performance due to heat: The whole point of forced induction is to stuff more air/fuel mix into the cylinders. The more stuffed in the more energy can be harnessed into torque. But stuffing (OK - compressing) air quickly causes it to heat up, although its going to get hot anyway 'cos the whole engine and bay does. Hot air molecules have more energy so they jump about like little kids and this increases pressure (just like kids do for their parents). So any heating of the air being forced into the engine is effectively fighting back against your very intention of doing so and getting more performance.
As to B8 vs B8.5, the cooling system was redesigned in the B8.5. IIRC a radiator was deleted but the charge cooler was changed from single-flow to dual flow. I guess in theory it was supposed to be saving cost but maintaining the same efficiency, but maybe not in practice. Of course Audi didn't design either cooling system to cope with tuned engines...
first para - still didn't get it though 
. Jokes aside, this is very very helpful
@Dippy and explains the whole thing, precisely what I was looking for. And it will now help with the data log I am looking at getting from OBD Fusion, which I know is not perfect it is just the right level to start for a novice like me. And I might be asking for some more guidance on that or perhaps steal one of XPs logs from one of the threads.
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