Nice write-up so far Tim!
The E4200 v2 indeed has the best USB read and write performance, as expected given what cNet observed.
I am glad the RT-N66U did very well in the WAN to LAN and LAN to WAN testing, albeit not chart-topping (that title still belongs to its predecessor the RT-N56U) and that it has more than enough total simultaneous throughput ("more than anyone could ever use" as you put it) and maxed out the simultaneous connections test.
Looking forward to the wireless performance tests in Part 2.
I think that, at least on the 2.4 GHz band *, wifi performance is where, based on my comparison tests and those of Geraner and others on amazon etc., it will hopefully excel overall relative to other N900 competitors.
I know you don't test / post signal strength which is what impressed me so much but hopefully the throughput figures in your tests will be near the top.
* I have not tested 5 GHz throughput yet although the signal strength on my Blu-Ray player's built-in dual band wifi adapter was impressive even in the far corner of the house (better than my E4200 v1).