I have experimented with tire direction in the past with the GP4000, Super Sport, and Ultra Sport and found that it made absolutely zero difference in the rain or dry as far as grip goes. It also made zero difference in rolling resistance and noise.
I also experimented with the Conti 700x38 City Ride and found it made zero difference in rolling resistance and grip in rain or dry. One difference that was noticed was noise, but that was it. Not sure why there are rotation marks on tires with seemingly little to no tread other than to legitimize the "sipping" tread design, although it seems to not matter in the least.