Ben. . suggest you do your home work before making a statement like that... there are several very good electric ones out there now. .
also remember that an Impact is intermittent use so it uses less air than alot of air tools do and the compressor can easily keep up with it... especially when a reserve tank is used with it.
many 4x4 guys use electric compressors on 35,37,40 "ers on up with great success
both of the brands I mentioned above WILL supply enough air for an impact, also look at the Oasis brand spoken of here. .