My 12-28 arrived, so here's the reported aperture and magnification against focal length for all current Z DX lenses (the 16-50, 18-140, 50-250, and 12-28).
First, the aperture reported to the camera:
I've included the 24-200 in this one with values taken from this post (I don't have a copy myself).
And for macro, here's the minimum frame width (along the long edge of the frame) possible on all the DX lenses and the 40mm:
Surprisingly, the 24mm keeps up with the zooms. Most are best at their tele ends, except for the 16-50 which gets closest at 35mm.
Theses were all measured with the camera pointed at a ruler. 1/4 grid lines turned on so I had a nice line through the middle of the frame to align the ruler with, and a focus confirmation point in the middle of the frame to indicate when the edge of the ruler was in focus. Generally shot wide open, I don't care enough to measure the effect of focus shift on these.