I like beam weapons, but from experience, I've noticed that they tend to do much worse than cannons. So I did some testing. I did many tests, but this is the one I want to show you.
This is my beam weapon...
216 total size
Main - 108 - Damage Beam Computer
Slave - 108 - Damage Beam Computer
This is my test setup...
The beam weapon is in sector 8,102,11
The cubes are in sectors 8,102,11 and 8,103,11
This is the damage to the cube in 8,102,11 (same sector as beam weapon)
This is the damage to the cube in 8,103,11 (different sector than beam weapon)
The beam weapon seems to do far less destruction after crossing a sector border. Also, I lined up my weapon on the target and pressed "V' to make sure I was stationary and not moving while firing. In the above pictures I performed 4 shots on each cube. And the cubes are using green standard armor and thruster blocks.