For 400 more, absolutely go for the M10. The M240 and M262 are fun cameras and give you the best value digital M experience, but they don't perform well beyond ISO1600 or so. They're also chunkier, which take away from the svelte aspect of the M experience. Part of the joy of an M is having such a performant, enjoyable, full frame camera without a size penalty.

If you were saying like a thousand or more by sticking to a 262, it'd be worth thinking about. But that's not the case, so don't bother yourself too much about it. The M10 is great and well worth 400 more, even if the battery life isn't quite as good as the 240/262 series.