I’d test a couple things:
1.) If you connect only one LTE WAN that is performing 160/20 on it’s own, what speed do you get with speedfusion with only one wan connection connected? I’d expect around 80% of the 160/20 due to the overhead.
2.) What happens if you turn off speedfusion, connect all three lte wans in a loadbalanced setup, and do a multiple stream speedtest?
From the spec sheet if I’m reading it correcctly, the 305 supports 1 Gbps of stateful firewall throughput but only 150 Mbps of speedfusion/pepvpn throughput.
Another thing I thought of trying, but haven’t yet, is to arrange clients in groups. Run multiple speedfusion tunnels, and assign group A to speefusion tunnel 1 with speedfusion tunnel 2 is standby, group B to speedfusion tunnel 2 with speedfusion tunnel 1 as standby and so-on in order to utilize multiple LTE connections and get the advantage of an unbreakable connection if one goes down or is impacted. I haven’t had time to test this idea though for myself.