i think alot more comes into play other than simple equation, not saying it is not use-able. But...consider these things also,
1. When you do BB you dont use as many stabilizers
2. Are you standing? Cause you may "pop" the weight with your back/legs if so allowing for a bit more power.
3. Range of motion. DB will change it, and if you go to deep, bye bye rotator cuff.
But yes, guess n check, but be reasonable in doing so.