Just for fun, I wanted to see the effect of an ND64 filter on a cloudy day during biking (as in "bicycle"). It definitely has some dreamy feel to it due to the motion blur, especially when I look at the road. The ISO was locked at 100-200 everything else is auto. As a result, it gets a little dark in the wooded areas but I think the EIS still does a farily decent job especially when the road is not too bumpy. Originally at 1080p/30fps.
Slowing the shutter messes up the stabilisation, best avoided unless you are doing some more static scene.
If you want a darker look better to adjust exposure when editing, NDs are best avoided with it for various reasons unless it is crazy bright like sun on snow or beach maybe
Good test you did there.
With ND64 and ISO 200 it will have about 1-2 stops under exposed giving the EIS a bit to work with, and it was not too bad.
I think OA3 is only suited to be used with CPL filters, since ND filters when in motion makes it struggle too much.