This archery thing is starting to sound like the "Enterprise vs Star Destroyer" arguement. We need to inject some facts here.
I feel like a STR 3. RAW says I can usually lift 45lbs over my head. I can handle a 65lb compound bow comfortably.
If that relationship holds, a STR 18 troll can use a 385lb compound bow as easily as I do a 65lb one.
A guy who posted on Yahoo Answers suggested a hunting arrow should be 10 grains per pound of draw weight. That means a 385lb bow should fire 3850 grain arrow. That is slightly over a 1/2 lb.
Searchy... searchy... searchy...
Well, the best archery ballistics calc I could find wouldn't spec out a troll bow (385lb firing 1/2 lb arrows), but it did give me an "ork bow" (200lb firing 1000gr(65g) arrows).
The arrows would move out at 370fps and generate 303 ft-lbs of energy. That is about 10% less energy than that of a 9mm pistol bullet.
On a projectile that heavy, the difference between energy and momentum may be important.