X2 on what Spressomon says... I have a 10lb powertank and love it. My father has a 5lb and a 10lb. They are faster than fast when you need to air up. However they do have drawbacks. Their cold weather performance leaves a lot to be desired. Also finding shops to fill them up is becoming a pain. When I first got mine, a fill up was $12.00. Now the shop charges $28.00 and you have to leave it. I wasn't very pleased about leaving my polished tank overnight with a fire extinguisher shop, but what else are you going to do?
I am looking at a hard mount compressor to be used along with the powertank.
p.s. If you get one, do not leave your regulator with the fill up shop.
I could also get quite a few fill ups with my 37's and my 10lb tank. Which would usually translate into me being finished a long time before everybody else and then usually filling up other guys tires to speed things up.