Expansion, I/O, and audio
Like many high-end Z270 boards, the Z370 Gaming 7 offers three PCIe x16 slots and three PCIe x1 slots, all meeting the PCIe 3.0 standard. Two of these are powered by the CPU's 16 lanes of connectivity. The topmost x16 slot gets 16 lanes from the CPU with one graphics card installed. Deploy a second card in the middle x16 slot, and the Gaming 7 splits those lanes into a pair of x8 channels. The third x16 slot gets four PCIe lanes from the Z370 chipset, and each PCIe x1 slot gets a lane from the PCH, as well.
For PCIe storage devices, the Gaming 7 has a whopping three M.2 slots, the topmost of which sits above the first PCIe x16 slot for better thermal resilience against the primary graphics card's exhaust. The first slot is also protected by a handsome M.2 heatsink with a pre-applied thermal pad.
Since Z370 is simply an evolution of Z270, loading up the board with expansion cards and storage devices could result in some resource-sharing conflicts. The first two PCIe x1 slots get a single lane from the chipset at all times, but the third shares its bandwidth with SATA port 0. Plug an expansion card into that slot, and SATA port 0 goes dark (or vice versa). Install a PCIe or SATA storage device in M2M_32G, the first M.2 slot, and SATA ports 4 and 5 turn off. M2A_32G, the middle M.2 slot, gets four PCIe lanes for M.2 devices at all times, but installing a SATA device in it will disable port 0, as well. Finally, M2P_32G (the bottom M.2 slot of the bunch) shares four lanes of PCIe with the bottom-most PCIe x16 slot. Install a device in one slot or the other, and its unused counterpart will go dark.
Those resource conflicts are a bit frustrating on a motherboard this expensive. The Gaming 7 only has six SATA ports to begin with. Use an NVMe SSD in the first slot as your system's boot device, and you immediately lose two of these ports to lane-sharing. It's a bit bemusing that Gigabyte didn't flip the allocation of lanes for M2M_32G and M2A_32G when it was laying out the board, considering that the middle slot doesn't ever conflict with SATA devices with an NVMe SSD installed. You can move the M.2 heatsink to this second slot, at least, but then you're subjecting your M.2 device to the jet blast of the PC's graphics card. This is a decidedly sub-optimal arrangement for the storage-hungry.
On the audio front, Gigabyte employs its usual arrangement of Nichicon and Wima capacitors in the board's analog audio path. The codec that feeds this array is Realtek's now-ubiquitous S1220 codec, complemented by an ESS Sabre 9018Q2C DAC. This chain is claimed to be good for an analog SNR of 121 dB, or on par with the claimed specs for many high-end onboard setups.
I had high expectations from the ESS Sabre DAC on this board, but the default voicing of the Gaming 7's analog audio chain is surprisingly low-mid and low-heavy, with distant, anemic highs. A little manual EQ woke up the potential of the system, however, and I was treated to an impressively wide soundstage, deep and expansive bass, and detailed, sparkly highs afterward. The Gaming 7 might be voiced for bass-heavy music by default, but I've never heard such an aggressive bias in any recent motherboard. Still, impressive sound is possible from this board with a tiny bit of tweaking, and it's definitely worthy of the price tag. Of recent motherboard audio I've heard, I'd say only that of Gigabyte's own Z270X-Gaming 8 is better.
The Z270X-Gaming 7 offers plenty of possibilities for peripheral I/O. All of the back panel's USB ports offer USB 3.0 speeds at a minimum. The leftmost yellow ports offer Gigabyte's DAC-Up voltage-control feature, which purports to provide more juice to power-hungry devices on long cable runs if it's needed. Although it's unlikely they'll be used on such a high-end board, Gigabyte offers an HDMI 1.4 jack and a DisplayPort 1.2 connector for Coffee Lake's integrated graphics processor, as well. The lack of a separate converter chip for HDMI 2.0 means the HDMI port only supports 4096x2160 at a maximum, and only then at 30 Hz. Those looking for tolerable IGP output probably want to use the DisplayPort, which can handle 4096x2304 displays at 60 Hz.
The two blue USB 3.0 ports to the right of the gold-plated display outs draw their connectivity from the Z370 PCH. The USB 3.1 Gen 2 Type-C connector and the red Type-A port both draw connectivity from ASMedia's latest ASM3142 USB 3.1 controller. Gigabyte backs this chip with two lanes of PCIe 3.0 from the chipset for a potential 16 GT/s of bandwidth, a reserve that might come in handy when transferring lots of bits over both ports at once. Above the Type-C port, we get a Killer Gigabit Ethernet jack powered by the company's E2500 controller. If you still have a thing against Killer for some reason, Gigabyte accommodates with an Intel controller behind the second Gigabit Ethernet jack. The final USB 3.0 port also comes from the Z370 PCH.
Somewhat disappointingly for such a high-end board, Gigabyte omits built-in wireless connectivity from the Gaming 7. The company's $200 Z370 Aorus Gaming 5 includes Intel's Wireless-AC 3165 card built into an M.2 slot in the rear I/O panel, an ideal arrangement that doesn't require burning a PCIe slot on a separate adapter. Not everybody wants or needs a wireless card built into their motherboard, but I feel like the Gaming 7's features should be a strict superset of Gigabyte's lesser boards given its price.
In a bold nod to cases of the future, Gigabyte dedicates an entire two PCIe lanes to another ASMedia ASM3142 USB 3.1 Gen 2 controller for cases with front-panel USB 3.1 Gen 2 ports. Outside of a couple of monstrous and monstrously expensive cases, however, USB 3.1 Gen 2 front-panel ports are a rare feature on today's enclosures. I applaud Gigabyte's forward thinking for this arrangement, but I also lament the fact that this connector (and its precious, precious chipset lanes) will likely sit unused in most systems.