In general head heavy racquets give more power, while head light racquets give more control on the ground strokes.
If you purely want power you can put the lead at 12 o'clock and you'll notice a considerable difference in power especially in the serve and smashes. However I warn you this leads to lot less in control you'll notice when hitting groundstrokes. Balls may often fly on you if you dont get a good connection with the ball. So I dont necessarily recommend it. You should basically do trial and error see what you are most comfortable with between the 12 oclock position, 10 and 2 position and 9 and 3 position or 6 position. 10/2 position will raise the sweet spot of the racquet if you tend to hit on the higher portion of the racquet. 9 and 3 will give more stability to the the head but still make a head heavier racquet for more power. Adding tape to the 6 oclock position wont add as much power, but it will maintain the weight balance better.

Another option if you want to maintain the control, while adding weight and power to the racket (assuming you are strong enough) is adding some lead underneath the grip on the sides as well and possibly add less to the head. Also if you have a light weight ounce scale and a balance board Id also recommend you keep the racquet weight balanced according to the factory specifications for maintaining optimum feel and control.

I often may switch to a racquet I weighted more head heavy on my serves to get the extra 5-15 mph on my serve, and then switch to a head light racquet on returning serves to get the extra control. Also use caution when adding lead to your racquet, too heavy of a racquet can lead to bad strokes and also tendinitis.