From the reviews that I've seen of the WNDR4000, the main complaint seems to be that the wireless speed falls off more rapidly with distance from the router than it's competitors. This may have been a firmware problem that's also been remedied?
On the other hand, I haven't experienced any wireless slow down over time with the Linksys E4200, but maybe I've been lucky. Been using the E4200 for several months now, aside from a brief interlude with an Asus rt-n56u *smile*. The Asus just didn't work out, sometimes that happens *smile*.