i have ftth network 800/200 Mbps (FTTH router -> EA8500 -> 1Gb switch -> rest of network), WAN speed tested with speedtest site, maybe here is the problem? How can I test that the result is reliable? maybe i will test this later without linksys router, only FTTH router and PC
EDIT
ok, i have changed some settings like @NamesAreAPain wrote
echo 35 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
echo 10 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
and tested some servers on speedtest net. few of them worked with full speed 800/200 
it looks like not all servers on this site are capable to test such speeds
btw. cpu in htop when i tested full speed is only ~50% usage 
https://www.speedtest.net/result/8304808443.png
thank you for help