How to get the max performance of nvenc on Quadro p2000?

Hi,I test nvenc on Quadro p2000, the number of streams of 1080p-420-8bit-hevc is more less than posted on the nvidia official website.
I use NvEncoderPerf on centos7.2, the cpu is E5 2680 v4, the comand line is “./NvEncoderPerf -i /ssd/year_1080p_1000.yuv -o out0.265 -size 1920 1080 -codec 1 -preset hq -fps 30 -goplength 50 -bitrate 8500 -rcmode 2 -devicetype 2 -inputFormat 0 -deviceID 1 &”.The memory and GPU occupancy are less than 50%.