The 4311CI is the next level up model with a more powerful power supply capable of driving 4-ohm speakers without additional amplification and predecessor to the current flagship 4520CI, and therefore better construction than the X4000 as well as capability to expand to 11.2; however, they both feature the same Audyssey MultEQ XT32 and Sub EQ HT and the X4000 has some newer features not present on the 4311CI (eg. Zone 2 HDMI, Instaprevue, DTS Neo:X, etc.). So it depends on which better meets your specific requirements.
I own a 4311 and wouldn't trade it for a new x4000. Like JD said, it's more comparable to a 4520 than a 4000. I use 11 channels and will never downgrade to less. neoX would be nice to try out, but I don't see it being much different than audyssey dsx. Just adds a few ambiance channels.