Haven't found a single range test video done in a big city. Every single Mavic range test video I could find is done out in the wilderness, or very small towns, and places with sparse population.

Unfortunately that does not apply to my situation. I live in orange county, california. Lots of interference. My Phantom 3 Standard could only go about 0.4 miles, and that was with that tin foil reflecter thingie on the controller antenna.

Gotta know the range before I buy.

It would depend on your location. If you are taking off from the top of a building with line of site between your controller and the Drone you will go a lot further that 0.4 miles but if you have large building directly between the Drone and the controller you are going to have limited range.
I haven't really found much interference from buildings as long as there is a direct unobstructed line of sight between the drone and controller.

I know you don't wanna hear it, but I say it anyways: The range in a big crowded city has to be the LOS at max. Good to know that you didn't found any test...

Haven't found a single range test video done in a big city. Every single Mavic range test video I could find is done out in the wilderness, or very small towns, and places with sparse population.

That's probably because most people get relatively poor results in urban areas, which makes for uninteresting videos. As The Rev suggested, the top of some building is probably your best bet -- and I seem to recall that I have seen at least one distance test video that was controlled from the top of a tall building in a densly populated area.

Unfortunately that does not apply to my situation. I live in orange county, california. Lots of interference. My Phantom 3 Standard could only go about 0.4 miles, and that was with that tin foil reflecter thingie on the controller antenna.

Yeah, the parabolic reflectors. They're useless (at best) with the Mavic, so don't bother trying them. On the other hand, you might benefit from something like this, but there's no guarantee. And to some extent you'd be sacrificing the controller's portability in the hope of getting better range.

Gotta know the range before I buy.

Nobody's going to be able to tell you that since there are so many factors that can affect the range. The best anyone could do would be to say "My Mavic got D feet away from me before the signal was lost while I was standing at location X, Y and flying at Z feet AGL on a heading of H." I understand that you'd like to know this and sympathize, but every situation is different and the reality is that some locations just aren't conducive to flying drones.