[Brightcolours]

Having two 70-300CX in the house tells all, doesn't it?! It is far beyond any other modern 70-300 lenses I've used in sharpness, not least in its long end (outclassing my 80-400 VR II easily, a at least twice as expensive lens, to my dismay, so that is now sold).

 

I have never found any problems shooting with them at 300mm (not worse than any other 300mm lens), as DOF is governed by actual focal length, not equivalent focal length.

DOF is "governed" by apparent aperture size (and equivalent focal length when you are comparing different setups).

 270mm f5.6 on FF -> 100mm f2 on Nikon 1. Similar FOV and same DOF.

Apparent aperture size: 270 / 5.6 = 48mm. 100 / 2 = 50mm.