Two Counts on a 5/2 opening. 1 Count on a 3/4. The exception would be of course if your opponent avoided Count/Duke altogether.
The reason for going for 1 Count on the 3/4 Split is that you want to get those Duchies ASAP. And, if your opponent buys a Count, that is a turn he could have bought a Duchy. A Count has to reach 1 reshuffle first. So, I believe that if you go for 1 Count, you will might win the Duchy split. But, I guess we really need to see what the simulators have to say.
One time though, I did open Count on a 5/2 Duke board. My opponent conceded.