We have almost identical size wrists.. I went for the 42, but... I never tried them on before.. haven't even seen an Watch in person. Hope I made the right decision. I also wanted a bit extra battery life.
You should get the 42mm.
I have 150mm wrist and 50mm with and I am still wantinf the 42mm.
And photos are lying.
I did a comparsion photo to show you what I mean.