I've heard of some problems with the Neo2, regarding them "stealth overclocking," running the HTT link at 4x and then upping the FSB to make up for it, which could cause a lot of problems with memory.
Anyways, NF4 brings a lot more to the table, like SATA-II support (you can now use NCQ and TCQ for newer hard drives), reduced CPU overhead for the hardware firewall, ntune (great overclocking tool, supporting multiple overclocking profiles for different situations like movie watching, gaming, etc.), and most of all, PCIe EXPANSION SLOTS! PCIe video is useful only for an upgrade. PCIe x1 slots are far more important, since they will allow for a generation of peripherals that are not possible on PCI. Creative's Zenith sound cards, SATA-II & III controllers, better HDTV recorders, etc. Also, reviews of the Asus and Gigabyte boards show that they can substantially outperform both the NF4 reference board and previous generation mobos, like the K8T800 Pro and NF3 ULtra. All in all, with these boards due before christmas, I'd say wait a bit.