I can also confirm that formatting to 4kb clusters improved USB writing speed to about 18MB/s.

Not only that, it saved a lot of space for me.
Before formatting every file below 64kb still took 64kb of space.
And since there are thousands of such files (cache, config files and especially map files) they took a lot of space.
Now the minimum file size is 4kb instead of 64kb and the amount of wasted space is a lot less.

Before formatting I backed up the whole mydocs partition to my pc so I didn't lose anything.