What settings should I use for formatting a usb drive that I am using to hold clones of virtual machines?

I have a usb drive that I am looking to use to hold clones of my virtual machines. I am already leaning towards NTFS over exFAT for robustness and some apparent performance issues with exFAT. But what should I make the allocation unit size? I do not intend to use this as a “regular” flash drive, so I want to make it larger than the default 4KB. My VMs vary in size though, and I am not sure how high to jump to make the performance better. How different will 8KB be from 2MB?
Any advice/insight would be helpful!

(Also for my own knowledge, is the “allocation unit size” just the hardware block size? I thought that was determined by hardware and not software?)