Here's some eye candy:

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Side-by-side Garrett (left) vs Precision (right):

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Precision has a slightly larger compressor wheel inducer (the visible part): 58 mm vs 56 mm

Precision has a slightly smaller turbine wheel exducer (the visible part): 62 mm vs 64 mm

The biggest difference is the shape of the turbine housing. The Precision very clearly has a smaller, more "tightly wound" shape that causes the exhaust gasses to more squarely hit the turbine blades. I can't find any A/R markings on the Garrett's turbine housing, but the Precision is marked as 0.58 A/R. The Garrett's A/R is almost certainly larger. Read about A/R here: http://www.turbobygarrett.com/turbob...housing_sizing