It all depends what you're keeping, and how much rock-work you have... My setup (Reefspace 900, 60 USG tank) has minimal rock-work, and soft corals: adding a pair of RW8s resulted in a sandstorm and all the frags pulled into one calm area at the back of the tank, on anything past setting 2. However had I been keeping SPS on a rock-work-heavy wall, then setting 2 would have been woefully inadequate.
Give us a bit more info on what's in your tank, and I'm sure you'll get some good advice!
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