Sorry but my reply was not driven by fairness. It is a fact. Look again at the bold-ed part. It is 100% wrong. And I have never heard of "effective hitting weight". Would you be so kind to elaborate on it?
I will. If you were to hit the ball at the balance point of a 320 gram racquet the effective hitting weight would be 320 grams. Of course, the balance point is usually in the throat so you can't hit it there. The further the impact of the ball from the balance point the less effective mass is present at that position. This is simple physics. The effective mass is still quite high at the bottom of the stringbed and gets progressively lower at your near the tip.
The intrinsic power of a racquet, known in physics as the apparent coefficient of restitution (ACOR) and at TW University as "Power Potential", is proportional to the effective mass, or hittingweight, at any particular location. In turn, the hittingweight is roughly proportional to the swingweight for shots hit along the longitudinal axis. For shots left and right of the axis, twistweight (polar moment of inertia) also comes into play, but swingweight is still dominant. Hoop stiffness is also a factor on off-center impacts, especially for those near the tip. Effective hittingweight for any location on the racquet face is easily calculated, provided you know the static mass, balance point, twistweight and swingweight of the racquet.
You can use this tool to find the effective mass of any frame:
http://www.racquettech.com/store/learningcenter/lc_effectivemassgeneral.html
So, does adding mass to the handle increase intrinsic power? Using that tool, we can look at a frame with the following specs: 340 grams, 33 cm balance and 330 swingweight. The effective mass 54cm from the butt (21.26 inches) and directly on the center line for that racquet is 171.51 grams. If we add 10 grams to the butt, the new specs would be 350 grams, 32cm balance and 330 swingweight, and the new effective mass at the same location would be 171.66 grams, for an improvement of about 1/10 of a gram. This extra 1/10 of a gram would improve the intrinsic power such that a player might gain a tiny fraction of one additional mile per hour on his shots. In other words, adding mass to the butt of a racquet improves intrinsic power by an insignificant amount. If we put the same 10 grams at the top of the grip instead of the butt, we would gain about 4/10 of a gram in effective hitting weight at the same impact location, primarily because mass added at that location will increase the swingweight by a very small amount (about 0.6 unit). Again, this increase is insignificant in terms of the racquet's intrinsic power, as anyone who has played with two raquets varying by less than one swingweight unit can tell you.
However, adding mass to the handle could change the way the racquet swings for a particular player, and perhaps for you this leads to a slight increase in racquet head speed and thus faster shots. But this has nothing to do with the intrinsic power of the racquet, as another player may have the opposite experience. Elementary physics, as well as controlled experiments with real racquets, shows us that the effect of additional handle mass on intrinsic power, or ACOR, is insignificantly small.