Don't know if this question is still important or already solved...
Here is my opinion:
Even if you have a tiny little air compressor - they deliver enough air for a 425+ lb.ft air impact wrench. I Might shock a lot of people now whit what I've just said, but here is the explanation and I also tested that:
If you have a huge air compressor but a tiny little Air impact wrench it takes you about 10 seconds to unbolt one Bolt at the wheel.
300 lb.ft flows 2.3 cfm (snap on) @ 10 seconds = 0.38 cubic feet of compressed air per bolt.
If you take a high performance impact wrench with about 575 lb.ft. It only takes about 2 seconds to unbolt one Bolt at the wheel, because the first couple of impacts brak the bolt loose.
575 lb.ft flows 4.2 cfm (snap on) @ 2 seconds = 0.14 cubic feet of compressed air per bolt.
0.38 vs. 0.14 cfm!!!
This means: If you only need an Impact wrench for a short ammount of time (not more than a couple of seconds), a big Impact wrench on a small compressor works just fine. It actually works a lot better than a small impact wrench on a medium size compressor!
To answer your Question: instead of buying an expensive electric one, I'd rather be buying a cheap compressor, and a powerfull Impact wrench (425+ lb.ft campbell hausfeld work just fine).
Keep on cruisin'
