I looked up the stats for the bows: Divinity 2: Ego Draconis All-Purpose Guide.
For DKS/D2:DC, there is also the Dragon Knight Saga FAQ/Guide.

I avoided using malachite gems in D2:ED and DKS (except for a couple level 10 healing auras), hoarding them in case I ran into trouble later, and not wanting to 'waste' them by enchanting equipment and finding something better soon after. In DKS I ended up with 65, though (about 27 at the end of the D2:ED section), so if I ever do another playthrough (unarmed), I'll be much more liberal with their use.