The compressors that I have seen with the Firestone kits are about as low end in performance for what is out there. Air bags don't need much, so there is no reason to supply a high end compressor. I have had two. One was 100 psi at 30% duty cycle and the other 150 psi at 30% duty cycle. and they were both 150.
If you are looking for "portable air" I'd suggest for 110 volt one of the Porter Cable 165 psi pancake compressors.
Reasonable priced for a fairly good compressor. have one of the older 150 psi units. 150 psi, because of the cut in cut out limits really doesn't work well for 110 psi tires.
http://www.amazon.com/PORTER-CABLE-...d=1384090251&sr=8-1&keywords=porter+cable+165
A 12 volt recommendation, is either a ready made package or an al-a-cart system starting with one of the higher spec'ed Viair compressors.
Here is the Viair catalog, price them out on Amazon.
http://www.viaircorp.com/viair.html
If airing up tires is your concern, what pressure do you have now and what pressure "may" you get in the future?
If I was buying a new 12 compressor now because of my up to 125 psi tires, I would look at one of the 100% duty cycle, 200 psi compressors.
Keep in mind most compressor cut off switches have a 35-45 psi range. And a 150 limit is not always 150.
So a 150 limit switch would typically turn on at 105 psi and off at 145 psi. Filling tires with those limits is time consuming.
I run a 200 psi compressor with a 175 switch. This means my compressor, at the lower range, is still filling the tires.