US1: 12 getworks per minute target
US2: 16 getworks per minute target
US3: 20 getworks per minute target
See which one works best for you.
So, mining with 1 5970 and 2 BFL mini rigs the results are:
US1 @ 12 getworks == diff between 50 and 75
US2 @ 16 getworks == diff between 40 and 50
US3 @ 20 getworks == diff between 30 and 40
I am really liking US3 with almost 1/2 the diff of US1. This has definitely helped bring share variance down and the swings in the diff changes as the server re-targets the diff.