We have a Balance380 with 5.4.7 build 2423 firmware. We do not use any kind of group policy QoS. We have two WAN links:
Fios at 150/50
Cable at 50/10
Today, a user was downloading software updates from our Fios connection at about 75Mbs, and this caused CPU load to spike to 100% on the router. Admin page requests started to fail and internet generally became unavailable to other users on our network. The the 380 should be able to sustain this throughput without falling over.