I deleted 12 apps this morning to get myself over 3 GB free in preperation of it, then ended up having to quickly delete 19 more to get myself to the 4.6 GB. I feel bad for anyone who needs 5.7 GB and is on a 16 GB iPhone. That seems tough.
Seems that 5.7GB are needed during the install/unpacking the update. The actual update will add the 1.1GB to your OS size, which on the 5s, seems like it will take up 4.3GB of space - not nice for "16GB" phones