We just finished this itinerary at the beginning of July in a forward balcony cabin 11710 and we LOVED having the balcony. We are Canadian but IMO we had the most beautiful amazing weather, not even any rain in Geiranger . The only day we really didn't care to use our balcony was the day we crossed the North Sea from Norway to Iceland and only because of the wind. Even on the days were the seas were a little rougher we barely felt any movement, we felt it more in the aft than anywhere else.
TRUST ME you want a balcony for the fjords, plus with such high mountains on each side you don't get much wind in that passage at all the water was like glass it was incredible. It was nice not having to stay up late/get up early in the mornings and stand on Deck 8 to watch sail in/sail out, we got a Starbucks or a cocktail and enjoyed the view 🙂
I think our coldest day was in Akureryi, it was 10C with some wind and every other day I was sweating to be honest, even Reykjavik was 17C and sunny 😳