I've really not seen anything to prove it performs any better than say Guarder Powerful at those temperatures. I tried to run my M4 at the start of this year and it was pretty horrible - it has a fully steel bolt and it's the WA system so it's not the most innovative thing ever, but I can say that the Powerful gas did perform better than the 3.0 (don't think their 4.0 stuff was available at the time). I mean Smart Gas sells itself as being a 'low temperature gas' on the can, but it's sure as hell not close to Nuprol 3.0 or Guarder Powerful in terms of power.
The bit about it working between 3-10 degrees isn't backed up by anything but the claim on their can and Facebook page. As far as I can tell the Guarder Powerful stuff is just that - more powerful and the larger cans are compressed even more. Although this probably isn't that case for you, it does disappoint me that Nuprol's very basic advertising pitch has been eaten up so readily by so many people. We've seen their BBs are naff yet people still buy them, and I don't think their regular gas has ever been any better than, say, Abbey Ultra.