I also own the GT-AC5300 and if you want an A+ Bufferbloat you need to set your values for qos upload, and download manually for the most part. You can typically set bandwidth to about 80% of what you actually get when running a full speed test. However, every network is different. If you run adaptive qos you have a little less control. If you have traditional qos you can implement as much control to bandwidth and paremeters as you would like. It really helps regardless to have a good stable internet connection that isn't riddled with jitter and line issues. But yes it is very possible to achieve an A+ with the GT-AC5300. I have been able to get an A+ with my netduma as well as with my GT-AC5300.