Where in /proc or /sys can I find the current bit rate?

[David Goodenough]

I know that I can get the rate using iwconfig, but that involves parsing
the response and I would rather not do that if I can avoid it.  But it 
occurred to me that most of the other values available through iwconfig
were available in either /proc or /sys, so I hoped that I could find the
current bit rate there too, but as yet I have not found it.  Anyone got
any idea where it might be?

David