This thread reads like a "how to make things complicated for no reason at all".
Avoid having to buy a bunch of separate filters and unscrewing all the time when the light changes.
Just get yourself a Fader Vari ND from Light Craft Workshop. It's one of the best investments you can make. Regardless of what camera you own today or will use tomorrow.
The original Fader Vari ND was already a great filter, the newer version seems to be even better.