I'm most interested in long runtime. I'm confuses between the two because the 4sevens website lists significant improvements in runtime with the S2, but I think I remember readings somewhere that this is based on a different testing standard. Can anyone verify if the S2 is notably better in terms of runtime. Also, I've read the S2 is greenish. Is this true of the X also? I want to order one as soon as I get this figured out, so thanks ahead of time for any feedback. I'm leaning toward the S2 based on the 4sevens listed runtime numbers.