I did some testing with multi-threaded enabled.
Same laptop: Thinkpad T430. Windows 7, 8GB, i5 3320M. Intel 82579LM Gigabit, Centrino Advanced N 6205. right next to router
Router: AC66R runnin Merlin 380.57
With 1Gb ethernet: 18Mb down
With 5Ghz - 16Mb down
With 2,4Ghz - 15Mb down
All tests pegged the CPU in my router.
Interestingly. I used my HTC One M8 to try the Lite tests on my 5G channel and saw 64Mb down! And router CPU was only about 50%. So is there some kind of difference in the traffic coming from my Lenovo vs my phone that is causing the router to work much harder? I'm not very network savvy, but maybe my laptop is making more work at the packet level for the router??? What can I try next to investigate?