Advantage AP in SM mode

We are about to do a MDU which is about 3kms from our NOC,my intention is to use a radio connected to a Cisco 2950 switch and hardwire from this to clients WRT54GL Routers,with the possibilty of around 40 clients,I know if for the radio I use a SM then it will only be good for 3 concurrent Voip calls,if I used an AP in SM mode would the unit process as an AP with 1500pps,or as a SM 300pps ?

An alternative would be to use a BH unit but I am getting tight on available non conflicting frequencies (5.4-5.7GHz) Can a BH master connect to two or more BH slaves ?