I'm currently in the midst of a long campaign as the Spanish. After I hit the high era, I started building xbows and arbs. But since I still have a lot of archers and a few merc longbows laying around I tend to bring a mix of both to my battles. I'm playing slow, and I've fought off a number of big attacks and rebellions. When I look at the summaries at the end of the battles, I find that the xbows/arbs kill a good number more men than the lbows/archers, despite the fact that the lbows/archers expend far more ammo.