i had a 7.25" wrist and wore a 45.5mm PO XL...now my wrist shrunk to below 7" so my PO also has shrunk to the 42mm.
but also note that the measurements for PO that omega states includes the crown guard.
so based on bezel diameter...the XL is 43.5mm, while for the 42mm PO it is 40mm.
that is also why most feel the 42mm PO wears smaller, as they expect a 42mm watch, but in actual fact it wears pretty fine.
now if you are willing to top up abit more, a good compromise is the PO GMT

anyway...this is a 45.5mm on my wrist.

and this is 42mm...yes...not a great angle...

but as can be seen the main difference is not really the size, but something not so noticeable unless its on your wrist - the lug to lug length.
the XL is about 52mm, while 42mm is a very wearable 47mm.