Isn't it so that Apache keeps a pool of children available and does not kill off these child processes after each request? If that is so (my experience is mainly with Apache on Windows) then adding the mod_deflate process to each child will only bloat the child even more and stress the server even more. Over the many years I am with Perlmonks now, I cannot remember that anyone has been able to point to the lack of bandwith as a cause of the slowness of the Perlmonks site and I even hazard to guess that the number of "slow" clients will be very small.
CountZero
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James