I went to smallnetbuilder.com at »www.smallnetbuilder.com/lanwan/r ··· rts/view
The EA2700 can handle the overall simultaneous upload and download fine. It is rated at 400Mbps combined upload and download. The WAN to LAN is 341Mbps. The LAN to WAN is 411.8Mbps. The details show that under certain circumstances you will be right at the limit of the router's WiFi performance. For example using 2.4GHz Uplink throughput at 40MHz B/W you get 36.2Mbps maximum capability. That is why you may need to use the 5GHz to take load off the 2.4GHz.
If you study the many charts you will see that the EA2700 surpasses the EA4200 in a few tests. The strange world of WiFi routers.
I would say it is a good choice for your situation. If you had the money I would try the new EA4500. I have used the E4200 with good results, but have not as intently as I think you will be using your router. I think the E4200 would do OK.