I am running a maya to mentalray command line render and am curious as to why I am only able to use 2 of my 8 threads (cores) when I do not specify -rt. Is there a way to default to all 8 cores? Also if I specify a thread count higher than the machine has will it overload the machine or scale back? For example if I specify -rt 10 on an 8-core computer will it scale back to 8, 2, or overload the system with 10?

This is the line mental ray is throwing out upon render:
Info: (mental ray) : number of render thread(s): 2