SSD, SATA vs M2 vs SATA Express

Hi!

There are some mother boards that can use M2 SSD's.
Or SATA to PCI-e..
In terms of speed the bottleneck is the SSD's speed.
But I think could be better a M2 SSD than a SATA one hanging over there.

Is there a penalty in performance using an M2 SSD in a GPU rig?
I'm thinking that maybe in the end they could be sharing the same bus as the GPU's, and this could be bad?

Any clue?

If there's another reason I'm missing why to use SATA SSD's, please tell me!

You can use a usb stick with an OS on it... No difference whatsoever using 3rd party miners

And cheaper than SSD's.

Do you have problems with writes to the usb stick?

Are you using ramdisk/full OS in ram?