Siguy,
Compared to some of us (well, OK, with
me), you are quite concise
This style is quite usable, and quite accurate. I am still learning it (and still throwing straight into the ground because I do not have my moves straightened out) but my ball or rock always goes straight toward the target (it just rarely gets there without a couple of bounces).
For me, after trying it for a week and reading what everybody else had to say about it, this works best:
Start facing your target, hands at or below your waist with the sling stretched between them, feet apart about shoulder-width.
Lift your right foot and take a step to the right, and twist your torso to the right, but keep looking at the target. Place your right foot almost at right angles to the target, and bring your weight over your right leg. The sling should now be pointing slightly to the right of the target. At this point you should look just like the statue, if you stop there and somebody throws flour all over you.
OK, OK, I'll be serious. Now, drop the rock from your left hand and pull back and up with your right arm. Start twisting back to the left, as your arm comes up. As your arm comes over your right shoulder, you should be taking a step toward the target with your left foot, and your weight should be shifting over to the left leg. Release the rock and plant your left foot. Or maybe they happen in the opposite order, I still am working on it.
Between the swing of your arm, the twisting of your torso, and the motion of your whole body toward the target as you step, this style should have a lot of power. But you have to get the timing right. Get the step and the swing out of phase with each other, and you will either drop the rock in front of you, or you will feel like you just stepped off a stair you did not know was there... very uncomfortable! This style seems very similar to the figure-8 to me, in this way: it is very awkward most of the time, but a couple of times I have accidentally gotten it right and it really works well! I will just have to work at it for awhile, same as I did with the figure-8. I gave myself a couple of bruises with that one, but now it is very natural, very smooth. I hope in a few more weeks the Bernini overhand will be as smooth for me.