Hi 502 Bob, Here's my compressor stat's; 10.3 cfm at 90 psi, 9.1 cfm at 135 psi. It kicks on at 95 psi and shuts off at 135 psi. Right now it has a 100-foot ½ air hose hooked up to it on a reel. Both ratchet and impact have a whip hose with inline oilers connected to them, the impact has a pressure feed in the handle, which I also fill from time to time. All the connectors are a commercial grade of Amflo 7's, that have large internal diameter. With the regulator set at 90 psi it never drops below that. I have an extra 20-gallon tank that I was going to connect to the compressor's 20 gallon tank but after four years it doesn't need the extra capacity using it for just an impact wrench. So I'm pretty sure that the ½ impact has 90 psi all the time. I hooked-up the ¾ impact the day I bought it and I noticed it "sounds" like it's turning slower then the ½, but I don't know as I have no way to measure it, unless I check-out the strobe light from work.
The reason I've asked questions on this subject is I hate to be stopped by a stubborn bolt or nut, and with impacts it's nice to simply hook up to the problem nut or bolt and blast it off. Like everyone else, I too have run into situations where I'm pulling on the end of a cheater bar and friends are trying to stop the other end from turning. So that's where I got the idea to buy a ¾ impact. I'll still turn up the pressure at the regulator, but if it helps a ½ impact deliver more torque it'll do the same for a ¾. Looking in a Harbor Freight and Grainger's catalogs, the ¾ impact I bought wasn't in there. I was hoping that the ¾ impact I bought had similar torque as the advertised stuff, in the 700 to 900 ft/lbs range, as that seems like a good step up in power to what I now have, (as you noted, 500 ft/lbs max). The ¾ impact looks like an over sized Dayton ½ impact with a power knob on the bottom of the handle. One good thing is the tip on running up the air pressure to more power. I was curious as to how much does that "Thunder Gun" cost?