I was asked a similar question by a customer a while back and was unable to find an answer either, apart from that if you are going to have a particularly high number of MAC addresses in the table it would be easier to place the list on a RADIUS server instead, just for the managability aspect if you have a large number of APs. Also I managed to dig this out of CCO, I believe from one of the recent wireless security documents... "there are a number of security problems inherent to using this method of access control. Firstly, as MAC addresses always appear in clear text, regardless of whether WEP is enabled, this allows them to be easily sniffed by an attacker. Secondly, most wireless cards will permit the changing of their MAC address via software." Having seen that, the customer was then fairly happy to consider the 'safe' options of access control.
If anyone does find an answer to the MAC address limit though, I'd love to know.
