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The Special Number Field Sieve factoring algorithm has a large number of parametric choices, each of which can affect its run time. We give guidelines for these choices along with a discussion of useful coding optimizations. We also give a theoretical argument which proves that the choice of sieving region that has been used so far in successful factorizations is not optimal and show how to obtain an improved sieve region. The improvement has yielded a 15% speed increase in practice.