With my camera set to manual focus at infinity, I varied my aperture from f/5.6 to f/8 depending upon the intensity of the lightning at the moment. I had the frame rate set for 30fps, although this didn't seem to matter too much because the camera was only really capturing an image when the lightning flashed. The rest of the time the frames were black from under-exposure.
One advantage to this technique was that I was sometimes capturing several lightning strikes on different frames and could easily combine them later in Photoshop by stacking the layers with the top layers set to a "lighten" mode. Since this was a fast moving video clip, the clouds stayed pretty much in the same position throughout making for a clean superimposition of images with no motion blur.
A disadvantage to this technique is that it limited my image size to 4k, which is smaller than if I have shot the photos as stills on the X-T1.
The samples below are combinations of 2 to 3 video frames combined to make each still image. Because my ISO was set to a low 200 and the clips were very sharp I was able to enlarge most of the images to larger than the 4k size with good success.
