Boards supporting x16 and x8 PCIe connections via electrical slots.
Boards supporting x16 and x8 PCIe connections via electrical slots.
There are options that meet your requirements. The Ryzen 7950X supports both PCIe x16 and x8 interfaces, though the physical slot widths differ. You won’t find boards offering all three types at once, but some provide x16 and x4, while others support x8 and x8. The 24 lanes in the chip suggest it can handle dual or higher speeds, though practical use depends on the board design. It isn’t limited to server or HEDT setups—compatible boards exist for various platforms.
The available lanes aren’t sufficient for running both x16 and x8 simultaneously. You’ll need a Threadripper or an Xeon W processor to handle that workload. While there are many dual X8 boards, they tend to be more advanced models.
Four of those lanes need to be set aside for an M.2 port, leaving just 20 regular lanes available. In theory, if the chipset handled something unusual—like the MSI X570S Ace Max did—it could work, but that’s rare in recent years. It’s also probable they’re constrained to PCIe Gen 4x4 speeds since data must pass through the chipset.
You require the 8 lanes for a specific purpose, but there could be other options that work better.
I'm searching for PCIe 4.0x4 QSFP+ NICs, but they don't appear to be available. They seem to be limited to x8 interfaces. It's possible some PCIe 4.0x8 cards can still function at 40 gigabit in 4.0x4 mode, though I'm not certain. Finding this information is challenging. Currently, my setup uses an Intel Xl710-QDA2, which needs to operate at half speed because it's a PCIe 3.0x8 card in a PCIe 4.0x4 slot.