It could probably be a lot less than 5%, 2% is more than enough I would guess, but we also need to reserve space to get good performance.
I'm more than happy to lose 3 GB on my 60 gb / 5400 rpm crap laptop drive and have reiser4 transform it into something that feels more like a big f*king raptor. Everytime I boot into Windows I feel the burning pain of this crap drive combined with the cancer of NTFS. Uh-oh this file takes long to load OH CRAP it's fragmented in 20000 bits (my personal record !). Gee. Gotta. Defrag. Again. Note that on your average Linux system with a zillion of small files the efficient reiser4 packing will save a lot of space. Un-tar the freedb database on a NTFS (or EXT3) partition and witness how your machine dies, then stop complaining about reiser4 eating 5% of your space dammit.
