4GB, 8GB - How much of that is usable space?

I’m sure this has been asked before, but I had no luck with a forum search or the FAQ/General Questions threads. How much space on the 4GB and 8GB clips is available for use? I’d like a precise figure because I’m considering picking up a 4GB Clip due to recent price drops, want to know exactly how much space I’d have to play with. I’ve been waiting for the 8GB Clip and its extra memory, but a cheaper 4GB might be too good to pass up if I can squeeze enough music into it. 

My 4GB Clip (v1 revision) properties show:

    Capacity: 4,090,875,904 bytes (3.80 GiB)

    Used:     2,063,355,904 bytes (1.92 GiB) 

for a total of: 

    2,041,024,512 bytes (1.90 GiB)

of media files stored. So, it seems there are about 21 MiB used by the system files, leaving a grand total of:

    4,068,544,512 bytes (3.79 GiB)

of actual data space.

Exactly what I needed to know. Many thanks!