I'm afraid I'm not quite technically trained enough to tell you the EV, but through trial and error I've found good results from - ISO 400, f/3.2, Bulb mode held open with a wired remote 'till a strike falls within the frame.
You need for the camera to be fairly sensitive (boost ISO and or fast apertures) because you can't rely on time since the flash is so brief. But you have to keep adjusting if the lightning is filling more or less of the frame, and also for how much your trying to show of your surroundings. Of course it all comes down to luck and tenacity (and knowing when to run away
). The
best lightning shot I've gotten was lucky in that a strike behind me lit up the terrain followed by the dramatic strike in the frame - worked out well.