What is the calling speed of outgoing directory?

hi to all
I m using Asterisk and I use outgoing directory to place automated calls and play a sound file.I have read that asterisk can handle about 250 simultaneous calls,but making 2700 calls and playing 35 seconds file takes an hour for me?Is it possible to increase the speed of outgoing directory or is it normal?I ve tried to set call-limit parameter to high value but it didnt work it s deprecated i guess.Then i read about groupcounters but i couldnt find how to use it.May someone enlighten me about this?