To add more power and stability, I recommend adding it to the 3 & 9 o'clock if you dont want the sweetspot to move up. If you want the sweetspot to move up, add to the 10 & 2 or the 12. However, the 12 makes it most head heavy. Wherever you put it on the head, you may want to counterbalance it by wrapping lead tape to the hande (take off the grips and wrap it around the grip near the buttcap. Then, put on a new replacement grip). You could put on a leather grip instead of a normal one like Wilson tru grip to add even more weight to the handle. I recommend using 1/4 on the head, or cut 1/2 really carefully in half. Use 1/2 on handle.
Remember, one inch of 1/2 weighs .5 g and 1 inch of 1/4 weighs .25 g. For adding tape to the head, a little bit heavier is 3-5 g and a great deal heavier is 10+ g. Dont put on longer than 6 inch strips. If you have to make it heavier in one spot, overlap with another layer.
Lead tape may strip the paint on some racquets, and some may not. On the one that I customized, the Ksix-one team, the paint didn't strip. I think that adding lead only makes pains if you make it too heavy and/or head heavy. & remeber, adding lead on the head takes away some feel from the racquet. If your a feel freak & need a hevy racquet with tons of feel, switch to a naturally heavier racquet such as the K90.
Heres a link to clarify, enjoy!
http://www.tennis-warehouse.com/LC/Customizing/customize.html
p.s., dont eat the lead tape