The B3 was the fixed chipset, it's still a p67 just one where the sata controller was fixed.
It just lacks the on integrated graphics (and the ability to use it for video encoding when using a separate graphics card) and the Smart Response Technology (using an SSD as a hard drive cache)
The p67 is no different on overclocking from the z68 as on SB overclocking is all down to cpu multiplier and the stability of the power from the motherboard VRM's
One thing the Asus boards have going for them is the very good automatic overclocking via their "Auto tune" where as the gigabyte auto overclocking system just uses a list of known safe overclocks and does a best guess based on the hardware detected.
Asus high end boards are good, however their lower end boards are not that good for the cost.
EDIT
ne of the other things the Asus boards have is the lovely Quick-sheild which is so much nicer to use than a standard IO shield, with no fiddly bits sticking out.
The Quick-connect is also nice but other brands also use them, the Q-shield is preparatory to asus, again doesn't come with the cheap models.
the P8Z68-V, Pro and EVO do have all these features, the cheaper P8Z68-V LE and LX don't