Have to disagree
I never really had a performance problem with the 120, found them a very nice aircraft to fly, very comfortable with a good view for pax and a useful size boot and good and stable in strong/messy winds.
There is however a big difference in weight between models. IIRC floats and VIP seats/soundproofing would add about 130kg versus and ex utility spec aircraft I used to fly which had seats added after original order. This equates to over an hours fuel or an extra person and a bit. So take a good look at the Gross Weight. Floats and bottles alone was, I think about 70kg.
I was a big fan, used them for most purposes. Didn't go wrong much, but when they did EC could be slow with support.