Don't pay any attention to HP ratings of compressors, the numbers are for the most part bogus. You need to chose based on the cfm needs of the tools you use. Even with a big tank it only delays the initial kick in of the compressor before you are stopping an waiting for the compressor to catch up if the cfm rating is too low.
The reason I say the HP ratings are bogus is because I have a small wheeled compressor that has label stating its 5HP but it plugs into a standard 15 amp 115/120 volt service. Just doing the math the most HP you can get out of a 15 Amp service is 2.4 HP and that is right at the 15 Amp limit. To run a 5HP motor on a 115/120 volt service requires about 40 Amps which requires special plugs, special wiring in the house/garage.
