It seems to me that many OCers rely on a CPUs stepping, sortof as an "OC-guarantee". However I'm not updated on this issue, and steppings that become high in demand are probably hard to get.
Concerning 2600s I don't know if there are two different versions (one with lower stock voltage than the other) as there are with the 2400s. The 1.35Vs have a product-id that ends with "FJQ4C" and the 1.45s have "FQQ4C". In theory the lower the stock voltage, the higher the OC.
AFAIK the only mobo in the NF7-series with GBLAN is NF7-S2G, but it lacks the soundstorm. You'll just have to weigh your need for high-speed LAN agains the sound, however there is one thing to keep in mind: Both the SATA-controller and the GB LAN is PCI-integrated. A configuration with SATA-disks and GBLAN would probably be stressful to the PCI-bus which has a b/w of 133 MB/s (that all components have to share). I have no personal experience in this, but you'll likely loose harddisk- and network performance this way, making the gain from 100Mbits to 1000Mbits LAN smaller.
Personally I'd buy NF7-S 2.0 as it is the No.1 OC-board. There are tons of modded BIOS's available and it's been tested and pushed and modded like practically no other piece of hardware.