Well, feel free to submit a patch. I'm just telling you that I don't believe making it more parallel will make anything faster, except maybe in some very contrieved example cases. But again, feel free to experiment. If you really manage to make my builds faster, I will not complain. 
I am planning to look into this when I have time (unless someone else gets there first
.
On my development systems, compile times under Windows are bound by both process creation and IO. Under Linux, they are bound by IO alone. No matter how many parallel builds I start (the sweet spot is 5 for me), CPU usage never comes even close to 100%.
Linking using ld literally causes millions of seeks on moderately large projects. Solid state and ram drives help, but do not make the problem go away. As such, IO is a dominating factor, and my guess is that adding more seeks does not improve the situation.
I am guessing the hardware I use is balanced very differently than that which you use (or maybe I just have not paid enough attention during my builds).
