I agree with Black_Zion here.
I have my CPU-NB running at 2600MHz as well.
According the information on the internet, it is rare for the CPU-NB to go much farther past ~ 2600MHz - 2700MHz. Beyond that will either become unstable, too much voltage is needed, or temperature is too high.
I thought my chip was slightly better than the rest, being able to run 2800MHz CPU-NB....but it turned out it is not 100% stable. It will only work sometimes.
Phenom II X6 1090T @ 4.1GHz FX-8350 @ 4.8GHz // ASUS Crosshair V Formula 990FX // Sapphire Radeon HD Dual-X 7970 @ 1150/1500 // Thermaltake Frio w/ push-pull (using Antec Formula 7 Nano-Diamond + Cooler Master JetFlo fans) // 8GB (2 X 4GB) G.Skill RipJawsX 2133MHz // Corsair TX850 850W // Corsair Force GT 120GB SSD (OS) // Kingston V200+ 120GB SSD // WD Caviar Black 1TB // Windows 7 Ult x64