mod_deflate: bandwidth vs processor cycles?

[Who8MyFish]

Hey, just looking for a little advise here. I have a couple questions and PHP freaks is packed full of smart people so I thought I'd head here after trying Google.

 

• at what file size you think mod_gzip/mod_deflate are useful and at what file size do you see a sort of diminishing return in load speeds?
  
• I stream .mp3 files with HTTP from this server, does mod_deflate or mod_gzip compress ALL traffic or just text files? .html .php .js etc.
  
• any other little pro tips I should know?
  

 

Thanks!