I don't think the USG Pro-4 is going to provide you with the bandwidth you have. I'm sure it won't if you enable QoS or IPS/IDS.
We use the USG Pro-4's at work and I use Untangle at home. The USG is a piece of garbage compared to Untangle and I HATE having to resort to JSON Hell when doing even basic things since the interface doesn't support it. The picture below is with a 25/5 DSL connection and it is using 44% of the CPU currently. Sometimes it is closer to 70%.
I can't wait for our Gigabit Fiber connection so get here so that I can convince them to replace the USG's.
Untangle HomePro is $40/yr and worth every penny imo. The TunnelVPN app is great and the OpenVPN app is easy to configure as well.
I haven't used pfSense very much so I will refrain from commenting on it.