X9 is for Direct X9 - XP, Vista, 7. X10 is for Direct X10 - Vista, 7.
X10 has better graphics simply because it's on DX10 rather than 9. However, TGC has dropped support for X10. With the newer updates X9 can produce a game similar looking to X10.
Remember this, making the game look good graphically is up to you, not just the engine.
There is no X10 demo, it functions the same as X9. As stated above, your last question makes no sense.
An answer to your question could have been found in one of the
many threads about X9 vs X10, by searching.