currenty i am using Ryzen 3500X
and total pppoe user is 720+
Bandwidth is 1.5G
my CPU is kinda hight average 20-25%
i would like to know if i upgrade my cpu to Ryzen 3700X
will it decrease CPU Usage ?
or suggest me other cpu model i dont want to change my mobo, currenty i am using B450 AORUS PRO WIFI
Is there any issue? You are not even using your existing CPU properly. 20% is low usage. When you get closer to 100%, only then consider an upgrade.
Come on Normis, do you actually wait until your bladder is 100% full before going…
For IT equipment the common line is between 30-70% utilization…
To the OP, get a Mikrotik device that matches your needs… you can buy a router and keep it for 5+ years easy… RB5009 for example).
don't worry ... there is a lot of headroom available still.
this kind of system surely also will not struggle much at around 80% load
at pick hour time ping time getting higher when cpu reach 20-25%
i want to keep it lower than 10%
By the second one so the average usage will be < 10% and you will have spare device in case of failure 
average CPU usage does not tell the whole story
watch every core usage
be aware that on x86 modern CPUS this metric can be mascarade because of Simultaneous multithreading (SMT)
if you upgrade to 3700x i suggest you to disable Simultaneous multithreading (SMT) on bios so you can see the real full usage on each CPU core
Simultaneous multithreading (SMT) only is really useful when doing rendering or encoding tasks, not when running a Router