Ahh yes I forgot about the broadcom hardware acceleration used on those routers. I use an Edge Router Lite from Ubiquiti and it also has hardware acceleration but with a Cavium ASIC. QOS does not affect the accel on that device(though bridging lan ports does...different discussion). I am not doing full QOS..I am just preventing my upload from ever getting maxed out. Very basic config.
I dont have specific numbers but from a PS3 standpoint I was playing COD Ghosts for several weeks hardwired to the CGN3 and had a lot of issues with lag spikes, slow matchmaking and sometimes not finding any lobbies at all due to high pings. This was consistantly bad...and very frustrating.
There was an instant improvement when I installed the ERLite and bridged the CGN3. I mean instant. I have had zero issues since.
The improvement was even noticable for simple web browsing from a PC.
For reference on a 250/20 connection. Rogers Speedtest with the ERLite shows 350Mbps plus with speedboost etc.
If you happen to have a laptop handy, can you follow the procedure outlined by dcowan38, log into the CGN3 in Bridge mode, determine its address and then ping the CGN3 through your router to see what the result are?