As Eric mentions, this is very difficult to predict without knowing a LOT more information regarding actual sites, clutter in the link path, distances, interference levels, etc.
All of that said, however, NLOS in an urban environment does perform fairly well with the 450 and 450i product platform. It is a 2x2 MIMO product, and dynamically adapts to modulation modes that will provide the optimal throughput to the device given the rf path conditions that are presented in the link.
For typical "urban canyon" deployments, multipath reflections can help to provide adequate signal levels to overcome NLOS conditions (i.e. the signals bounce off neighboring buildings). There will be no difference to the system, as each link is modulated independently, so it should not matter to the system how many subscribers are being utilized. The only consideration there is that in a multipoint system, the Access Point or sector capacity is a shared medium, that is you share the overall capacity between all subscribers attached. Therefore, if many heavy usage subscribers are operating in low modulations, then your overall capacity is lower.
There are many threads in the forum that discuss this "shared media" concept, hope this information helps.