Beefing up a 727 trans!

What about ATI racing transmissons? Looked at their selection and it isnt bad at all. $922 dollars for a 727 or 904 trans with reverse manual valve body or $1542 for the same thing but with a trans brake. By the way... what is the difference between a 727 and 904. I heard that the 904 is lighter but not stronger. Is this true or just a myth?