How many users a single asterisk can support?

I am confused, since on the DIGIUM Knowledge database there is two different technotes… One of them states that ABE (Asterisk Business Edition) support 240 simultaneous calls on a 2 CPU machine…

The other one, talks a maximum of around of 80 users, if GSM codec is used and echo cancellation… I do not known if so a huge difference is due to ABE 1.2 and Asterisk 1.4 differences, or the difference is based on the codecs used…

I am sure that loads depends on codecs being used, transcoding… but seems a lot of difference…

For example, on a configuration on a powerful machine, with 2 CPU, how many internal calls could be done (I guess no transcoding needed netiher echo canceler)? How many external (using PRI) ? Is there any difference if ABE 1.2 is used or a normal Asterisk 1.4 ?

I have to deal with a large installation for 700 users, but they do mostly internal calls, and no more that 30 (a single E1 line) externally… I am worryed about Asterisk being able to deal with such number of users, even on a powerful machine… And if possible, want to avoid to introduce OpenSER or additional machines…

It is really hard to say how many calls a sever will handle. There are a lot of possible factors such as codecs, compression, recording, will the rtp stream being go thru the box etc. This question has been asked on the asterisk users list many times. People have replied on what they have seen. Have a look at the users list @ lists.digium.com. Also for 700 concurrent calls I would look at OpenSER.