It's on the smaller side however wears like a 40mm watch, I'm very impressed. Could go to AP royal oak 39mm however I was recommended that it's not good quality from Ryan. The 15400 looks quite big and just too big on my 6.5 inch wrist
Not sure how much you can trim down. Caseback is where the issue is. There is a 1,X mm area that needs to be thinned for gen dimensions+look but with rotor+decoration it looks impossible to get further down. Loco louie apparently offered a thinned version but judging from his pics I don't see any difference to stock.