Quote: "Stability?"
X10 was very unstable for a long time. A couple of updates from Lee got the worst bugs out but the features felt incomplete or unexpandable.
Quote: "Graphics Quality?"
Great. X10 is a better place to start than X9 if you want good graphics out of the box. The tradeoff is we haven't seen many custom shaders or new shaders, if any.
Quote: "Community Mods?"
There is 1 to date. Its probably worth giving a try but I think its incomplete at the moment.
Quote: "Game Assets?"
Good. It comes with more characters than X9 and they are high quality.
Quote: "Documentation?"
Not good. You basically get the same manual as X9 without any of the meaningful X10 features being described. The community actually figured out how to get normal and specular maps working in the early days.
Quote: "The major differences between x10 and the x9 version?"
X9 is officially supported with a lot of community support (mods) and highly scalable. X10 is not officially supported, has a smaller user base but can produce better looking games out of the box.
Quote: "Difficulty in moving from x9 to x10?"
None if you dont count the lack of documentation and support.