And with all that, i can't even bring one ships shields down, let alone scratch the hull... either something is seriously wrong with my weapons, or i've found a big bug in the game
Most likely it's a power problem; either you're not putting enough energy into weapons, or you're running out of energy too fast with five beams.
I personally would have one less beam in the back; either another torp to discourage tailgaters, or a mine launcher.
Some better engineering consoles could help with that, too.
Also, are you remembering to come out of full impulse well before you come into range? It drains all your power, you need to allow time for that to come back up before you engage.