Nice shots. I was out on a boat tour and it was lightning off in the distance, didn't have a tripod but managed to get 2 shots (that showed any lightning at all). I like how mine came out but the lightning is only a minor element in my photo. Incidentally, I probably fired off 1-200 shots and might have deleted a couple that had some lightning since it turns out I couldn't see it very well in the 60d display. I saved one just because of the landscape and it turned out there was a lightning strike when I viewed it on my PC.
Anyway, my method--since I didn't have a tripod, and the boat was rocking anyway (if I did), long exposures weren't much of an option. I was curious and wanted to see what happened if I tried, even a 2-3s expsure at F9 was getting washed out from the lightning lighting up the sky. My handheld shots that came out were at 1/6s, iso 800, and f6.3.
I'll have to try again with that/your method, some solid ground, and a tripod someday. Again, those came out very nice!