I wrote this up on my blog, where I can intersperse text and graphs a bit better:

Basically, I ran a series of tcp_download tests, using increasing ingress rates with sqm_scripts, and then used flent's box-plots to put the results into a combined image for comparing.

On the 3800, it never meets the rate, but it's only off by maybe 5%.  But on my new WRT1900AC, it's wildly off, even over the same performance range (I tested it from 80-220Mbps rates in 20Mbps jumps, and saw from 40-150Mbps.

I have no idea where to start looking for the cause.  But for now, I'm just setting my ingress rate MUCH higher than I should, because it's working out to the right value as a result.

-Aaron