FYI for anyone else doing this type of build ... moving my GPU to PCIEX16_2 slot (because it no longer fits in PCIEX16_1 due to a poorly place motherboard display unit) means my water cooled front/rear 4090 GPU will only be able to run X8 and not X16.**
I "assumed" that a $1000 motherboard would:
Allow for full coverage water cooled GPUs to fit in PCIEX16_1 slot Allow me to select which one of the two PCIEX16 slots to run at X16
Unfortunately that is NOT the case, the ONLY slot this Asus X670E Extreme motherboard can operate at X16 is PCIEX16_1 slot (regardless of M.2 configurations).* That does beg the question why Asus falsely label the slot as PCIEX16_2 when it has no ability to run at X16 regardless of hardware configuration?
This is clearly a motherboard limitation as the CPU PCIE lanes are sufficient to support.
nVidia 4090 GPU (16X) PCIEX16_1 M.2 4X via Chipset (4X) M.2 4X via General Purpose PCIe (4X) USB 3.0 PCIe card (4X) PCIEX4
All within lane spec usage ... however because I moved the GPU to PCIEX16_2 this is what I'm forced with:
nVidia 4090 GPU (8X) PCIEX16_2 M.2 4X via Chipset (4X) M.2 4X via General Purpose PCIe (4X) USB 3.0 PCIe card (4X) PCIEX16_1
Really not happy with ASUS right now ... maybe other manufacturers do the same?* ASUS does NOT permit me to set PCIEX16_2 to 16X and PCIEX16_1 to 4X - why??
I don't know exactly how much this has impacted performance?* I was able to improve TimeSpy score both CPU/GPU to 32379 and very good temps with peaks at 58C CPU and 47C GPU under full stressed loads (but sorta expect that from a dual loop with one loop on a custom vapor chiller).
I suggest a riser cable (e.g. LINKUP do pretty good PCIe 4.0 ones) and front mounted GPU. That's probably better for thermals anyway, as the GPU has more space to exhaust and isn't exhausting directly on the motherboard and chipset, and it leaves a good airflow channel across the chipset heatsink that tends to be obstructed by giant GPUs. Full flexibility of lane allocation isn't simple for high bandwidth signals. It's not impossible, but not easy, and the long standing convention is that the top slot is the full x16 slot. The slots are labelled according to their mechanical/physical size, and the documentation is there for you to make an informed choice before purchasing. The lane configuration and slot labelling on the X670E boards is not really anything new, just the latest iteration of how it has been done for a long time.
Have you ever seen any mainstream motherboard that allows the second slot to run as x16? Honestly, I don't think they exist (not counting the former HEDT class boards, or the expensive pro workstation class boards (Threadripper & big Xeon).
I replaced the air cooler on my ASUS 4090 TUF OC Edition and replaced it with EK full coverage (front and back) water block ... airflow isn't a problem and temps are very good.
Actually, my prior ASUS boards were capable of setting X16 for either (not both at the same time) of the two slots (using Intel CPUs) ... and I think this is why ASUS still use the reference PCIEX16_1 and PCIEX16_2 and didn't update the reference when they decided to only support ONE and ONLY ONE PCIEX16 slot (PCIEX16_1).
This X670E Extreme is a $1000 board ... the most expensive board I've ever purchased. I'm NOT exceeding lane capacity per specification and since there are TWO X16 slots with support connectivity I should be permitted to simply designate one or the other as X16.
But, this wouldn't have been an issue if ASUS had provided a few more millimeters on the CPU side of the slot rather than consume the space with a redundant display ... this is supposed to be an "Extreme" board, not a bling bling board.