I'm 5'4", 115 lbs, and I'm using a backplate that I bought from NW Grateful Diver, who is considerably taller and bigger. It's fine. I think you only need to consider a different sized plate at the very extremes of body size.
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SparticleBrane:I believe the backplate issue might be more important for smaller people than for larger people. My girlfriend is of a small size, I believe she's...5'5"? Anyhow, a standard backplate seems just a tad too large for her, it covers her back and then some. She might be a candidate for a slightly smaller plate.