If the armholes are too high, that's an issue with the jacket that sizing up will solve- however, it looks like the rest of the jacket fits spot on, so sizing up would mess wih the rest of he fit. I would not size up, but return if the armholes are not confortable to wear.
The arm holes aren't uncomfortable or anything, they're just tighter than I'm used to with a jacket. Same with the chest area. I don't think I actually have any jackets right now with really high arm holes to be honest, but as I put it on more and more, I definitely am getting a lot more used to it.
It's definitely a bigger purchase, so I just wanted to make sure. I'm definitely going to hang on to the size 48 then I think. Cheers everyone for all of your input!!!