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A quick look at performance
If you've read our review of the Core i7-3770K, you know how its performance stacks up at stock speeds. You've also seen how much additional performance can be gained by turning the frequency up to 4.9GHz. At that speed, Ivy Bridge nearly matches the performance of the Core i7-3960X, which is based on Sandy Bridge-E silicon that offers two more memory channels and CPU cores.

So, what about the configurations we've discussed in this article? 7-Zip and the x264 encoding benchmark were run on all the boards at their highest stable settings. The Asus was tested with the CPU at 4.9GHz, while the others had it clocked at 4.8GHz.

100MHz amounts to around 2% when you're running at speeds this high, so it's no surprise to see all the scores so close. The Asus P8Z77-V generally comes out on top thanks to its clock speed advantage. However, it has the lowest frame rate in the second pass of the x264 test.

Overclocking on the sly
For quite some time, we've complained that Asus' motherboard firmware engages in overclocking behind the user's back. If a manual memory multiplier is set, the CPU's single-core Turbo multiplier is applied to all-core loads. The Core i7-3770K runs at 3.9GHz when all its cores are occupied instead of the default 3.7GHz. This constitutes overclocking, according to Intel, and it shouldn't be done without the user's consent. Even worse, it violates good practices for enthusiast firmware: modifying one setting should never change another, and especially not one that's completely unrelated.

Asus doesn't ask permission when applying this "multicore enhancement." The firmware's all-core Turbo frequency display is changed to reflect the overclocked speed, but the user isn't given an explicit message about what's going on. At least this feature can be disabled in the firmware; we just wish it weren't enabled by default.

When defending this behavior, Asus has insisted that other motherboard makers engage in similar dirty tricks. We didn't see any evidence of that when testing Z77 boards with a Sandy Bridge CPU. However, we did catch one more offender when we switched to Ivy Bridge. Gigabyte's Z77X-UD3H plays the same game with Turbo multipliers if the memory speed is set manually. Our Core i7-3770K runs at 3.9GHz with an all-core load when the memory is set to run at 1600MHz. When the memory divider is left at "auto," the CPU speed tops out at 3.7GHz when all cores are active.

Does the Gigabyte firmware ask permission? Nope. Indeed, nothing in the firmware even informs the user that the CPU has been overclocked. Although the status window displays a 39X multiplier for all-core loads, it does so regardless of the memory configuration—including when the board is using the correct 37X multiplier.

We haven't had time to grill Gigabyte about this behavior, which can only be corrected by setting the CPU's per-core multipliers manually. Ugh. It's hard to view this trend as anything other than an underhanded attempt to inflate benchmark scores. There's more evidence that Asus and Gigabyte are pushing boundaries, too. According to CPU-Z, the Z77X-UD3H's default base clock speed is 100.88MHz, while the P8Z77-V is clocked at 100.52MHz. I'm not going to get too worked up over sub-MHz increases to clock speed, but it's worth noting that MSI nails the 100MHz default exactly. The Intel board runs a smidgen slower, at 99.78MHz.