Rain-X do a screenwash additive as well as the standard product now.
If you do a lot of motorway driving it's amazing stuff. Wipers off at 70mph in fairly heavy rain as it all beads and runs off.
It seems to vary from car to car as to the minimum speed it works but in my experience you need to be going at 40+ mph for it to work.
Back with front wheel drive and 181HP at the wheels