My C: is a PCIe4 NVMe that hosts Windows11 and all my programs including the MSFS install but not the packages, apart from at the initial loading of MSFS into ram it basically stays idle while I’m simming. It’s my fastest drive so this is what I record to, 4k@60fps using either indistinguishable quality or lossless video compression and I can honestly say it never skips a beat. Mostly I’m using the NVENC, H.264 encoder although I sometimes use the software x264 (but not with MSFS as it uses the cpu more).
Hope this helps.
PS. PCIe3 would usually struggle with uncompressed 4k but could still be decent if it’s dedicated only to video, remove it’s page file if you do.