I own both of these planes and that’s what the manual tells you to do. They even include a weight box in the kit, so you can put all the led into it and close it up tight. You can down load the manual at the Tower Hobbies’ web site, it will say on page 30 that with an OS 120 four stroke the P-6E Hawk will need 16 oz of weight in the box to start with.
http://www3.towerhobbies.com/cgi-bin...&I=LXLDU9&P=ML
BOUND_4_HELL
You can never have too much power, as you can always throttle back.