OpenVPN and slow performance

i use for a lot of year wrt-320n (mod @e2000). Now i need more performance with openvpn and bought a new Linksys EA6350v3.
But also with the new router, i have slow performance; with iperf only 5/6mbit/s.
This is my config:
With top, cpu is always under 10%

config openvpn 'OpenVPN'
	option ca '/etc/openvpn/ca.crt'
	option ifconfig_pool_persist '/tmp/ipp.txt'
	option keepalive '10 120'
	option compress 'lzo'
	option persist_key '1'
	option persist_tun '1'
	option user 'nobody'
	option status '/tmp/openvpn-status.log'
	option verb '3'
	option port '1200'
	option dh '/etc/openvpn/dh.pem'
	option cert '/etc/openvpn/cert.pem'
	option key '/etc/openvpn/key.pem'
	option server_bridge ''
	option tun_mtu '1500'
	option cipher 'BF-CBC'
	option tls_server '1'
	option fast_io '1'
	option client_to_client '1'
	option duplicate_cn '1'
	option enabled '1'
	option dev 'tap0'

Do u have any suggestion?
Thanks in advance

Try another cipher like aes-128-cbc or aes-128-gcm and probably you have a lot fragmented packages due to your mtu of 1500.

If you have a dsl connection, you will only have a mtu of 1492 on your line and then the vpn encapsulation needs also some bytes.
With fragmented packages, your router has to split your oversized packages into two packages which is very costly in cpu power.

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