Bungeecord high cpu usage

I heard something somehow being done multi bungeecord and its reduce cpu usage.
whe i have 700 player cpu is overloading too much, "htop" shows %600 cpu usage.
but when 500 player htop shows %200 cpu usage, what is this reason ?

i have only bungecoord on my lobby server but even this cpu overloading Intel Xeon E3 1245v2 (4 cores / 8 Threads)