[Milhouse]

IMO EXT4 is slightly faster than F2FS in Reads and much slower in Writes.
I can't really say I notice any difference in library browsing.
There's a significant performance increase in installs and updates as well as restoring backups.

That's pretty much borne out by my own testing and also confirmed by phoronix who concluded that ext4 is the fastest filesystem when reading (ext4, f2fs xfs, btrfs in descending order of performance) but f2fs is fastest when writing (f2fs, ext4, btrfs, xfs in that order).

When first setting up a system it seems that f2fs would be the best filesystem, as you'll be generating lots of writes while scanning and caching, but once the system is up and running ext4 would be the optimal filesystem. As it's not possible to use both*, I'd stick with ext4 as it's more stable and has better read performance which is what you'll be doing most of the time.

* Putting the SQLite databases (which will be written frequently) on a small f2fs partition and everything else (/storage, thumbnails etc.) on ext4 might be the best compromise solution and may be possible with path substitution (or symbolic link) of the Database folder.

EDIT: I've confirmed that its certainly possible to create two partitions - one ext4 (for /storage) and the other f2fs - then move the Database folder to the f2fs partition and sym link /storage/.xbmc/userdata/Database from ext4. The f2fs partition will be mounted automatically by OpenELEC, using an automatically constructed mount point (eg. /var/media/sda2-usb-_USB_DISK_3.0_07) but it may be easier to remount with -o noatime and use an easier to remember mount point (eg. /var/media/f2fs) - this can all be handled in autostart.sh. The system boots reliably (which is a problem I had when using f2fs as /storage) but I'm not really sure if there's any significant benefit - there's probably some, however if you are using MySQL (as I am) the benefit is likely to be minimal and not worth the effort.