Wet and Wides sizing:
It ok to buy wets pretty long. Buy what ever size you want but this is a recommendation in my opinion. If you want the longer ski buy a longer ski. It's 6cm it won't kill you it is a bit big. If you are heavy or ski fast, sizing up is a good idea.
If you are under 5 6, probably 171
If you between 5 7 and 5 9, probably 177
If you are between 5 9 and 6ft, probably 183
Taller than 6ft, probably 189
Keys:
Keys run true to size so you don't have to size up unless you want to. Again, just get the size you want that works best for your style.
