Recommend placing the soul trap effect first this ensure that you trap the soul if the enemy dies from the sword hit. As I understand it's some problems here. 2 seconds is also long enough, 1 second longer than the damage effects.
Agree with this. I've had to sell some bows that just didn't work out well, as I had the soul trap effect last, and at the same time as the damage effects. So I always now put Soul Trap as the first effect, and one second longer than the heaviest damage effect and it works out really well. And one other tip regarding bows, Soul Trap at 3 seconds or more, on your bow, is useless for an archer character. I've already got another arrow ready on my bow, but must wait one precious second to see if my previous shot is the killing one. And, I found I was wasting arrows, a bummer if you are using enchanted ones. So for a primarily bow person, Soul Trap at 2 seconds is long enough, you could go to three seconds, but then I would be using heavy poisons and high-damage arrows for that kind of bow, think: shooting slower for higher damage. I tend to shoot a little faster than 3 seconds inbetween my shots.