m.2 assist mb
m.2 assist mb
You're looking for guidance on setting up your first PC build with a MSI B850 Edge Ti motherboard. The specs indicate support for PCIe 5.0 x4 in all three M.2 slots, which is great. Based on the information you provided, placing the third drive in slot 4 should work since it's faster than slot 3. The speeds from the chipset will match those from the CPU, but ensure your drives are compatible with PCIe 5.0 x4 for optimal performance.
What drives are you using, and what's the use case or them? That can have an impact on it. That's probably what I'd do. Whether it would matter would depend on what you're trying to do though. There is a latency benefit on the CPU slots, not really raw bandwidth. That said, even in synthetic benchmarks it's hard to measure, so in practice it doesn't really matter, it's just theoretical that the OS drive is better to be on one of the CPU slots.
If all drives are X4, the best slots are 1, 2, and 4. There are also X2 drives available. If you get an X2, placing it in slot 3 would be logical since it wouldn’t gain the extra lanes in slot 4.