which ride are you looking at? You will likely need the 164 MINIMUM but probably the 167.
WTF? Why would he need such a big board? That's ridiculous. If you want an all mountain board that will still perform in powder just get a hybrid rocker/camber board. There are plenty of options that allow you to do all the things you want without having to buy a mega board. A board similar to what your using now would be a rossignol krypto which is also a mid wide if you are concerned about boot size.