Speed between SDFS(FAT16) and SDFS32(FAT32) from the guy that modified SDFS for FAT32.
Compared to SDFS, SDFS32 should access the SD cards at almost the same speed, maybe a few microseconds difference here and there.
The speed difference really comes into play when dealing with large files. Each sector read or write has to traverse the entire FAT cluster chain. The larger the file, the longer it takes to access a sector.
In other words, for example, writing 1 sector takes 1 ms. Appending a 2nd sector might take an extra 1.1ms, a third sector takes another 1.2ms, and so on.

Kinda like writing a book. Only instead of turning the page to add another page of writing, each time you want to add another page of something, you have to close the book, reopen the book, and re-read thru everything you've already written to find the end, before you can start adding stuff again.