If you are going to do as I have during testing and push this board nice and hard, you'll need ample cooling. ASRock provided me with a Bitspower full-cover copper block (nickel-plated) to help keep temperatures in check. This block covers both the CPU socket and the board's VRM, drastically reducing temperatures all around even when you install a CPU like the crazy 18-core i9-7980XE (which I was sure to try out to see how the board would handle it). ASRock also provided Bitspower's Leviathan Semi-AIO kit, which features a copper radiator and flexible clear tubing with pre-installed fittings all nicely packaged separately. The pump/reservoir combo is attached to the radiator via a metal bracket, with the radiator dumping it's cooled coolant directly into the reservoir.
The full-cover block is ready to support the add-in card in front, which actually screws into the board's provided VRM cooler to help keep the small thin board from flexing. I did find that a bit of tension on the front-panel USB 3.0 wires can make this card twist quite a bit. In fact, I was worried I had broken it as I had bent it quite a bit by mistake, but was fortunate enough to not have damaged anything. Do make sure you are careful with this part as the front add-in card is attached to the system using the tiny socket you see in the second picture above, and that socket sits directly "below" that problematic USB 3.0 header.
Once installed into the case with cooling attached, the ASRock X299E-ITX/ac has a huge presence for such a small board. I think the provided cooling plays a big part in it, though. I really like how the default LED color closely matches the mainstream colors ASRock has chosen for their board products and that of the writing on top of the LAN ports, which identifies those ports as being driven by Intel controllers. It just fits together so nicely and shows the attention to small details ASRock has with all of their products.
You can see that the chipset cooler is exposed to airflow when your VGA is installed, but you can also see that the front-panel audio header might not be in the most ideal location, but that's what happens when you squeeze everything into such a small space. The mass of wires coming out of the board - the SATA cables, 24-pin plug and front-panel USB 3.0 cable - all clump together in one area towards the right edge of the board. This will affect airflow over the board's VRM cooler should you opt to not buy the full-cover waterblock (but how could you NOT buy it!).
The ASRock X299E-ITX/ac has a very standard Turbo profile at stock, which is what you want to help keep power use in check on this platform in general. These CPUs can easily gobble up well north of 250W otherwise, but I found this X299E-ITX/ac to work just right.