If with "capacity and performance" you mean the maximum performance an EAP225 can achieve under ideal conditions, this can be easily calculated from the figures in the data sheet for EAPs. If you mean the best performance of an EAP at a given location, this could be only measured by doing real performance tests with professional measurement tools such as NetSpot or iperf.

If you rather mean the actual bandwidth used by clients over a certain time span, this is mostly useless information because it depends on so many factors such as the type of the client devices, the wifi rates negotiated between each device and the EAP (which changes constantly over time according to the usage!), the distance to the EAP, interferences from other devices, the amount of AirTime allocated by each device etc. and - most notably - the usage pattern of the user.

As for wifi rates in Mbps currently negotiated between a client device and an EAP, see the Clients statistics, it's listed there. For me, this is the most important characteristic for a wireless link to a particular client device. But wether the user of this client actually makes full, half or no use of this wireless rate available for his link isn't of much interest to me.