I had the same dilemma, also 165mm wrist, but I went with the 42mm instead. That was months ago and I still question if I made the right choice sometimes 
I think 165mm wrist sizes are in a weird spot. We can pull off either size, but have to choose to go a little too small or a little too big. The whole reason for that is because of the the width of the watch! While the 38mm height is perfect, the width is actually only 33mm. Meanwhile, the 42mm is a bit too tall, but the width is perfect at 36mm. Round watches don't have that problem but because it's a rectangle, one side will always be longer than the other.
Overall though, I think you'll be fine with either. Here's some of the 42mm on my wrist with a few different straps if you're curious. If it makes you feel any better about your choice, that 3rd party milanese loop wraps almost all the way around nearly touching the top lol, looks kind of dumb.
I think 165mm wrist sizes are in a weird spot. We can pull off either size, but have to choose to go a little too small or a little too big. The whole reason for that is because of the the width of the watch! While the 38mm height is perfect, the width is actually only 33mm. Meanwhile, the 42mm is a bit too tall, but the width is perfect at 36mm. Round watches don't have that problem but because it's a rectangle, one side will always be longer than the other.
Overall though, I think you'll be fine with either. Here's some of the 42mm on my wrist with a few different straps if you're curious. If it makes you feel any better about your choice, that 3rd party milanese loop wraps almost all the way around nearly touching the top lol, looks kind of dumb.
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