This is a photo of mine. Not the Outback but it will give you an idea of the size.
The Givi Trekker 46L (the bigger one on the left) is advertised as 310mm deep.
The Givi Outback 48L is advertised as 306mm deep.
Bigger volume but 4mm narrower.
The Givi Trekker 37L is advertised as 246mm deep.
Mine at a total width are 112cm across, the same width as my wing mirrors (Aprilia style on extenders).
That is a 52L top box, try not to put too much heavy stuff in there though.
I think the 2017 has the low exhaust so you can fit the same on each side, I like the two different sizes to even the width out on mine. (plus SHMBO can get more in the bigger one!!!
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It's good to have the room but you might/will end up taking more than you need.
I can filter fine with that set up most of the time, but I don't do town/city centres, I'm talking motorways/dual carriageway filtering.