I just finished mine and it comes in at ~8.8lb dry. I am using 9411s on the surfaces, a 2300mAh 6V battery strapped to the wing tube, and a EVO 1.20 and Bisson pitts muffler. The EVO is 1oz heavier than the saito 125 with a pitts on.
As for the balance, I was able to balance it perfectly the ~170mm mark perfectly with a half tank of gas with no weights added eight off the bat.
Since the tank is located in front of the wing tube, the CG will shift around as the tank empties but I remember this was not a real problem with the X100.