This is my usual weapon. Rend and Tear.
http://imgur.com/a/VdhuL
For the Crossbow, the arrow speed is the most important part for damage. Second would be reload speed (boosted by redstone) to repeat fire faster.
nice one! I'm trying to progress to thaumcraft to get some thaumium, not unlocked yet. As soon as I unlock that quest chain and get thaumium I'm going to destroy dragon. Still need to set up power plant+production chain. Never played with railcraft/mekanism before and it was too long ago since I played with BC. Stuck on a couple quests (god dammit hate mariculture -.- ).