Varies greatly based on encoder. NEVC vs CPU etc

Not asserting this isn't the case, I've not noticed it, but I can't see why this would be the case for the actual encoding. Decoding I've seen it make a difference but that's mostly the pre-Skylake iGPUs using a poor implementation of QuickSync.

Honestly, for normal people things hard drive is hard drive. If it's a hard-core high-performance DATABASE, always spinning ZFS pool then MAYBE it'll matter. But for just storing data, like a normal use case, heck even a heavy normal use case like photo/video storage where you're caching on an SSD for editing but fairly intensely reading/writing back to the drive, it's fine.

The only time it'll probably matter is if it's someone else's money, then just get the expensive drives so you don't get blamed (enterprise), it's some super intense database or something, or Security systems there are some benitifs for a drive designed to be CONSTANTLY written to.