This is just what I have found in my opinion. Feel free to disagree below.
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 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.