I bought the E4200v2 when it first came out. About a year after having it, it stopped working all together. Linksys sent me the refurb E4200v2 that I currently have over a year ago.
I am on a 70/6 plan with my ISP. I have a PC wired to the E4200v2, and a Mac and a PC wireless (along with a phone, tablet and Roku).
My iMac is the main machine that I use. I use it on the 5GHz band. When it's working properly, I get around 70/6. However, it slows up drastically by itself almost 4-5 times per week (it doesn't lose connection though), and the only way to get back to around 70/6 is by turning my iMac's WiFi off and then on again. I had the same issue with a PC (on the 2.4GHz band) that I used to have wireless. I had to constantly disconnect and then connect again to get a decent speed.
The same thing happens with the current wireless PC. Also, the 2.4GHz is pitiful, as no matter what I set it at, the most I can get is around 30/6. I've adjusted the wireless setting many times to no avail.
Finally, a similar thing happens to the wired PC. Except that I have to reboot it at times to get around 70/6.
Maybe with the new firmware that I just automatically received, these issues will be helped. I'm going to check it out the next few days. If these issues are not fixed, I have my eye on the WRT1900AC.
Sorry for the long explanation