I must be honest, I did not see a huge difference in picture quality between the 7000 and the 6900, the real difference is the black filter, which is a help if you have a window nearby or want to watch during the day a lot, so not an additional expense I thought was worthy of £200ish.
I looked at the PX990 but at the time it was also £200 more than the 6900, I preferred the finish of the samsung, but the LG had slightly better Black levels.
It's a though one, the 6900 got 3D TV of the year, but if I was you I would try to audition both and see which you prefer. I love me 6900 by the way.