The default is to have the file size (the -s option) be twice the size of RAM which will usually be enough to break all caches. But if you need to test other things (like filesystem performance with big files) then feel free to make it as large as you wish.
When you use the -q option stdout gets the CSV format (as shown in the above question) and the human readable version goes to stderr. To convert the CSV version to human-readable use bon_csv2txt.
In the human readable form what you call "IOPS" is called "Random Seeks".
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