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Performance highlights
When they're equipped with the same components running at the same speeds, motherboards typically have little impact on system performance. There are rare exceptions, so we still run a range of application and peripheral tests on the boards that pass through our labs.

Unfortunately, a strict apples-to-apples comparison escaped us here. We're using Corsair's Vengeance LPX DDR4-2800 memory in our Haswell-E test rig, but due to firmware multiplier limitations, we can't run it at top speed in the X99-UD4 without boosting the base frequency to 105MHz. That might seem like a small increase—it only raises the peak CPU frequency from 3.50GHz to 3.68GHz—but Intel CPUs are typically very sensitive to changes in their base clock. Our test system isn't entirely stable with a 105MHz base frequency.

The other X99 board in our stable is Asus' X99 Deluxe, which has the multiplier required to maintain stock CPU clocks while running DDR4-2800 memory. Rather than re-testing the Deluxe to match the slower DDR4-2666 setup we used on the UD4, we decided to compare the two configs to see where the slight difference in memory frequency might affect performance. Here's how it impacts a targeted memory bandwidth test:

Surprisingly, the bandwidth gap is a little wider than one might expect from the change in memory frequency. Yet the two boards produce identical results in many of our performance tests:

So, yeah, nothing exciting here. The Gigabyte config is a smidgen slower in a few instances, but it actually comes out slightly ahead in x264 encoding. It's been a while since we took an in-depth look at the impact of memory speed on application and gaming performance. Perhaps it's worth revisiting the subject with Haswell-E and a wider range of memory speeds. Hmmm.

The results of our peripheral tests are mostly a wash, with the X99-UD4 shadowing its Asus competition virtually throughout. In most cases, the differences are no larger than the run-to-run variances for each board. That said, the Gigabyte has slightly higher random I/O rates with our PCIe SSD but slightly lower random I/O performance with USB 3.0 storage. By far the biggest discrepancy is in USB 3.0 random write speeds: the UD4 hits 147MB/s, while the Deluxe reaches 171MB/s. Sequential throughput is much more relevant for USB storage, though, and the gaps are much smaller in those tests.

Both boards exhibit low DPC latencies during basic music playback and a full system load. They also have similar analog audio signal quality according to RightMark Audio Analyzer's "loopback" test. We could make you scroll through a bunch of unnecessary bar graphs (again), but there's little point when the results are basically the same.

I guess graphs can help to break up large swaths of text. So, how about some boot times?

The X99-UD4 goes from power to the Win8 desktop 1.7 seconds faster than the Deluxe. That number may have some significance for a notebook or mobile device, but if you boot your desktop frequently enough for a couple of seconds to matter, you have bigger problems to address. And you should probably just be putting the machine to sleep, a state from which the UD4 awakes almost instantly.

For what it's worth, X99 systems boot 10-15 seconds slower than their Z97 counterparts. This sluggishness seems to be related to the extra initialization time required by the platform's glorious excess. By the time X99 rigs get around to displaying the POST screen, Z97 systems are already sitting at the desktop.

We've now covered the most important aspects of the X99-UD4. The following page has more detailed specifications in addition to specifics on our test systems and methods, but the giant tables and nerdy details are a little dry, so we won't blame you for skipping to the conclusion. Or you could bypass that agonizing decision and pay what you want to become a subscriber, which gets you a nifty single-page view. Just sayin'.