Performance issues with EdgeRouter POE

Hi all,

I've been trying to find the solution for this for a while now. Please note that this is my first EdgeRouter so I have probably done something wrong.

However - the issue is that everything works properly when I'm not downloading anything. The latency to the router (from within the network) is below 1ms on a wired connection (pc). But as soon as I start downloading (for example update games from within Steam) something isn't working properly. 

I have a 100/100 Mbit fiber connection and steam maxes out at around 16-17Mbit (never did with my old openwrt router) + that the latency to the router jumps up to around 150-300 ms from within the network. The webui is also unresponsive during this. As soon as I stop the steam download everything returns to normal. 

I can't really wrap my head around this so any help is appriciated.

Here is my configuration.

firewall {
    all-ping enable
    broadcast-ping disable
    ipv6-receive-redirects disable
    ipv6-src-route disable
    ip-src-route disable
    log-martians enable
    name WAN_IN {
        default-action drop
        description "WAN to internal"
        rule 10 {
            action accept
            description "Allow established/related"
            state {
                established enable
                related enable
            }
        }
        rule 20 {
            action drop
            description "Drop invalid state"
            state {
                invalid enable
            }
        }
    }
    name WAN_LOCAL {
        default-action drop
        description "WAN to router"
        rule 10 {
            action accept
            description "Allow established/related"
            state {
                established enable
                related enable
            }
        }
        rule 20 {
            action drop
            description "Drop invalid state"
            state {
                invalid enable
            }
        }
    }
    receive-redirects disable
    send-redirects enable
    source-validation disable
    syn-cookies enable
}
interfaces {
    ethernet eth0 {
        address dhcp
        description Internet
        duplex auto
        firewall {
            in {
                name WAN_IN
            }
            local {
                name WAN_LOCAL
            }
        }
        poe {
            output off
        }
        speed auto
    }
    ethernet eth1 {
        address 192.168.2.1/24
        description Local
        duplex auto
        poe {
            output off
        }
        speed auto
    }
    ethernet eth2 {
        description "Local 2"
        duplex auto
        poe {
            output off
        }
        speed auto
    }
    ethernet eth3 {
        description "Local 2"
        duplex auto
        poe {
            output 24v
        }
        speed auto
    }
    ethernet eth4 {
        description "Local 2"
        duplex auto
        poe {
            output off
        }
        speed auto
    }
    loopback lo {
    }
    switch switch0 {
        address 192.168.1.1/24
        description "Local 2"
        mtu 1500
        switch-port {
            interface eth2 {
            }
            interface eth3 {
            }
            interface eth4 {
            }
            vlan-aware disable
        }
    }
}
service {
    dhcp-server {
        disabled false
        hostfile-update disable
        shared-network-name LAN2 {
            authoritative enable
            subnet 192.168.1.0/24 {
                default-router 192.168.1.1
                dns-server 192.168.1.1
                lease 86400
                start 192.168.1.100 {
                    stop 192.168.1.199
                }
                unifi-controller 192.168.1.2
            }
        }
        use-dnsmasq disable
    }
    dns {
        forwarding {
            cache-size 150
            listen-on eth1
            listen-on switch0
        }
    }
    gui {
        http-port 80
        https-port 443
        older-ciphers enable
    }
    nat {
        rule 5010 {
            description "masquerade for WAN"
            outbound-interface eth0
            type masquerade
        }
    }
    ssh {
        port 22
        protocol-version v2
    }
}
system {
    host-name ubnt
    login {
        user admin {
            authentication {
                encrypted-password $6$4kKcy7K1VxORIyJ$EhfmIyv0j.Z/Nq3bRFGSmcm.Dxq.Bw6MLXo5SasY/KgXKHcNhrLcR66WDVpmBqk/J2.Hn2.37bJ9ogvRs3GB..
                plaintext-password ""
            }
            level admin
        }
        user ubnt {
            authentication {
                encrypted-password $1$zKNoUbAo$gomzUbYvgyUMcD436Wo66.
            }
            level admin
        }
    }
    ntp {
        server 0.ubnt.pool.ntp.org {
        }
        server 1.ubnt.pool.ntp.org {
        }
        server 2.ubnt.pool.ntp.org {
        }
        server 3.ubnt.pool.ntp.org {
        }
    }
    syslog {
        global {
            facility all {
                level notice
            }
            facility protocols {
                level debug
            }
        }
    }
    time-zone UTC
}


/* Warning: Do not remove the following line. */
/* === vyatta-config-version: "config-management@1:conntrack@1:cron@1:dhcp-relay@1:dhcp-server@4:firewall@5:ipsec@5:nat@3:qos@1:quagga@2:system@4:ubnt-pptp@1:ubnt-util@1:vrrp@1:webgui@1:webproxy@1:zone-policy@1" === */
/* Release version: v1.9.0.4901118.160804.1131 */

I'm using the latest version on my edgerouter and have only used the webui to alter any configuration. I started trying to configure everything manually - but then using the wizard for WAN-2LAN2. If I've missed any information that would help I'm happy to add it.

Any help is mostly appriciated. 

Thanks!