I guess a daily mean of 180 PPM, peaking at 500 with load of 6 on 4 cores.
Running at 200 PPM the load is about 2÷2,5, with most of it being disk IO latency (CPU wait time).
EDIT: BTW, I would try to further lower your VM memory, maybe to 4 GB, just to have a valid comparison and see if the load decreases. In case, you might consider using a different java VM with better CG.
Also, check what makes up the load. It might just be IO latency.