"The X470-F ROG Strix is based on the standard ATX form factor and features three PCIe 3.0 x16, three PCIe 3.0 x1, and two M.2 slots — a welcome improvement over the older X370 and B350 boards that featured only a single M.2 slot. We still do not know whether these M.2 slots are PCIe 3.0 x4 speeds capable."

I would ignore this as, to all intents, complete misinformation folks.

We do know am4 can't magically develop more pcie 3 lanes.

Many x370 moboS now have 2x m.2 ports also. One uses 4x pcie 3 lanes for full strength, the other is hald strength using 4 x pcie gen 2 lanes using the shared chipst bandwidth.

what is new, is the 400 chipset will allow slightly better half strength chipset m.2 port using 2 x pcie 3 lanes instead of 4x pcie gen 2 lanes.

Beyond the 4 lanes for the full m.2 and the 4 lanes for the chipset, there still only remains 16 lanes, usually used by the gpu.

For proper nvme raid, you would need to consider 8 lane GPU, which many argue is painless except for some high end games.

Pairing two vanilla nvmeS, one on the gimped chipset & one on the mobo, could still result in far better performance than the best single nvme drives, like the 960 pro.

Paired half strength $120 250GB Evo nvme drives, are much faster than a class champion $340 500GB 960 pro, especially write speed.

"fully backwards compatible" = how it should be done