Another X870e Lanes question

So with the numerous M.2 slots available (regardless of 5.0/4.0/3.0 capability), how do I find out which can transfer data between each other quickly/easily? And which would affect other lanes-users like the internal NIC, SATA SSDs or HDDs, WiFi, etc…

Example: Moving data between the Type-A 3.2 Gen’s … I think I’d need to be sure to use the one on the CPU and another on the Chipset to achieve the fastest transfer speed between them. Using 2 on the same chipset would hamstring the speed, right?

not following you here. Everything still goes though CPU, it’s the processor that handles all I/O at the end of the day (not talking here about specialized hardware offloading cards like DPUs). With this regards, the closer two devices are to the processor, the better. But this “better” is subjective. Measure and see if that makes a difference.

And which would affect other lanes-users like the internal NIC, SATA SSDs or HDDs, WiFi, etc…

This should be explicitly stated also somewhere in the manual. Something like “if you populate the PCIe x4 slot - this will disable the third slot M2_D” for example. Seek for * asterisks on every page

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So to that first point, with the CPU directing traffic, I should not have to worry much about data movements across storage media and their respective I/O interface.

I understand the lane sharing on the slots for AIBs or M.2 slots native to the MB. I was wondering if in a hypothetical I was using a 10G NIC in a PCIe4_1 x4 slot and went to copy a bunch of data from a M.2 on a riser card in PCIe5.0 x8 to a SATAIII HDD while making a duplicate copy of a 500GB file from the front panel USB-C on the case to a rear panel USB 3.2 Type-A , whether my 4k YouTube video I was watching would stutter.

I doubt it will. Grab a calculator and see yourself. 1 raw lane of pcie4 is 2GB/s (bigaBytes per second, not gigaBits). The Chipset-to-CPU interconnect thus 2(GB)*4(Lanes)*8(Bits in Byte) is 64 Gbit.
Well, it could stutter, but probably for a different reasons than lack of IO bandwidth.

Should be just fine. A 10 Gb USB’s 1 GB/s and Promontory 21’s good for ~6.5 GB/s in either direction. (Don’t have a board with two chipset M.2s, so haven’t been able to test for the full 13 GB/s bisection bandwidth, though.)