http://www.woodshoptips.com/tips/081902/page4.htm
Table 7-1: Drill Press Speed Chart
Size of Hole    Hardwood    Softwood
1/4" and less   H (1600 RPM)    I (1750 RPM)
1/4" to 1/2"    F (1300 RPM)    G (1450 RPM)
1/2" to 3/4"    D (1050 RPM)    E (1150 RPM)
3/4" to 1"      B (850 RPM)     C (950 RPM)
Over 1"         SLOW (700 RPM)  A (750 RPM)
Boring metals (twist bits only) -- Slow (700 RPM)
Note: These speeds are for 60 hz. operations.