Of guilds that are at least 6/13H, of which there are ~230 25m guilds, and ~450 10m guilds, there are 22 25H Lei Shen kills, and 42 10H Lei Shen kills. Of guilds that are decently skilled (6/13H is a decent qualifier because it forces guilds to have killed fights like Council, Primoridus, Magaera, etc), 9.56% of 25man guilds have killed Lei Shen, and 9.33% of 10man guilds have killed Lei Shen.
I can't make any objective judgements about the difficulty of Lei Shen on the two difficulties as I have not done 25H Lei Shen having gotten gear at the 25man rate, but it appears in terms of what percentage of the skilled heroic raiding community has killed the boss, that it is roughly even in terms of difficulty to complete.
---------- Post added 2013-05-11 at 09:46 AM ----------
---------- Post added 2013-05-11 at 09:47 AM ----------