Yves,
Client load calculation is tricky and depends on many factors. Client capabilities (radio quality, supported data rates, receive sensitivity, etc), the RF environment in the area, and the applications in use by the clients or bandwidth requirements all play major roles. All these things have to be considered when determining how many clients are too many in a given situation.
In a well designed high density environment 80 clients could be supported, but each of those 80 clients must share the bandwidth capabilities of the radio (i.e. 150mbps/80 =1.875mbps). So high bandwidth applications on the clients would be difficult to support (i.e video stream etc.)
Based on the fact that you said this is a 2.4GHz radio, and due to the lower bandwidth and RF challenges of the 2.4 GHz spectrum, I would guess that 80 clients are likely too many.
In order to support a large number of clients you need the following:
1. High SNR for clients, which allows for high data rates. The higher the client data rates the more bandwidth you can push through the AP. Even a single client communicating at 2mbps (data rate not bandwidth) can reduce the efficiency of the radio as a whole.
2. Low RF interference and minimal co-channel interference. This is difficult to achieve in the 2.4GHz band
3. Client applications that are low bandwidth and/or client rate limiting. This prevents one user consuming all the radio's bandwidth.
