Had a read of this thread one more time today and was thinking of another upgrade, this time more expensive but anyway:
from the following vehicles:
Mercedes Vito, Sprinter
VW LT
You can get the windscreen jets that are mounted to the wiper arms. I've been in a short ride the other dar in a Vito and these jets just work so well, each one has three nozzels that spreay liquid across the entire length of the blade.
I have found that after some years the washer liquid leaves marks on the paint around the std jets on the bonnet, nothing serious but it is quite observable.
You will get rid of that if getting wiper mounted jets plus no matter the speed you will always have the spray in the right spot.
I will post some pics when I'll be doing the mod, as far as it looks like it's not difficult do to, and yes, it will be fine on a mk3 (and any other car basically)