Sau is being used as a pejorative here. It is there to show your displeasure or disgust with something. A sew is a pig which usually are disgusting. Dogs as well.
Saukalt --> It's very unpleasantly cold.
Saugut --> It is very unpleasantly good.
The unpleasantly comes from the lack of other words to describe it. You have to go down to the animalistic level inside yourself to express the dimension.
Too good to just say: Ich mag es, das its gut. But rather you wan to say. It is soo magically good the devil must have messed with this, it's fucking good.
Sausauber --> Just sounds weird using the same syllable twice this way.
Sauschön --> Borderline weird. But again so pretty you cannot fucking describe this in another way.
Hundekalt --> same thing
Hundeschön --> makes no sense because the syllables don't match it is to complex to be said and to be meant seriously
If you don't want to use Pig or Dog you can use
Das ist abartig-schön.
This means this is uncommonly or unorderly pretty.
abartig = abnormal, deviant, unnatural
b (=widersinnig) perverse
So in German you can also say.
Das ist pervers kalt heute.
Das ist pervers schön.
Das ist pervers, dreckig, kalt, schön, hoch, tief etc.