I need to purchase an air compressor for a service truck i'm setting up.  

What are the pros - cons of an electric vs gas motor driven air pump?  I would also like to have a generator, to charge cordless grease gun and tool batteries with, so i'm at a bit of a crossroads -

John Deere or Mi-T-M Compressorator - 15 CFM 2-stage air pump with a 4500 watt generator all built as one unit - $2500

Or, buy a separate electric driven air compressor and generator.  This would be a bit less money, $330 for a 3500 watt generator and then I could get an IR 8 gallon single stage (wheel barrow type) honda driven pump for $900 rated at 11 CFM.

For an electric option, I could pick up an electric Campbell Hausfield 20 gallon tank, and mount that on my truck, and for $350 I have 5 CFM @ 90 psi.  Its a lot less air, but how much air does a guy need to blow off chaff and what not??

During harvest, I blow my combines off every morning, and could possibly pick up some cheap air tools to use.  Mostly tires and blow gun is all I use it for though - is 5 CFM enough?  Or is 11 CFM needed?  

Its a difference of nearly $1500 - 1000 bucks, so I'm obviously looking at my options.

Thanks,

Owl