I have an 80 gal 5hp unit from Northern and it runs almost constantly when I use my mud hog to cut filler; I'm about to pipe it into my 60 gal unit that went bad. So I'd definitely say bigger is better. Like stated especially if you plan to paint.
http://www.northerntool.com/webapp/w...1707_200311707
This one looks pretty close and a bit cheaper--- these units looked like nice units as well! Free shipping too!