With 802.11AC officially supported now (since the end of last year), I do not think that making a distinction between N and AC products is helpful in any way.
http://www.smallnetbuilder.com/wireless/wireless-news/32313-80211ac-specification-is-final
The main reason I suggested the RT-AC56U is because it has recently been seen at $99 on sale and it is also one of the top performing routers when comparing them for Total Simultaneous Connections.
http://www.smallnetbuilder.com/lanwan/router-charts/bar/76-total-simul
In the link above it is currently at #5 and while the RT-N56U is slightly above it; the ~$20 price difference between the two is insignificant when considered over the time of expected ownership (3-5 years).
The extra dollars buys you a current class product with superior wireless performance (vs. the RT-N56U) along with a better dual cpu SoC and more RAM.
When (not if) your devices start to support the 5GHz band and even better; the AC standard - your wireless performance will also jump considerably with the RT-AC56U vs. any N router out there (for the same or more money).
You may also want to consider the following charts for (wired) routing performance too to see if any current products might match your requirements better (though I don't think any will overall at the price point you set).
http://www.smallnetbuilder.com/lanwan/router-charts/bar/74-wan-to-lan
http://www.smallnetbuilder.com/lanwan/router-charts/bar/75-lan-to-wan
It may turn out that the OP is willing to buy an older/cheaper N class router that does have slightly better (wired) routing performance because it is that important to them - but my money would go with a current product that not only offers high theoretical speeds - but actually has the modern components to back them up with.
Including RMerlin firmware support for new features, bug fixes and improved performance over the official Asus firmware (which seems to get the RMerlin improvements eventually too, in time).
I'll repeat; imo, at the $100 price point (you may need to wait for a sale though) - the RT-AC56U is the best overall router to buy right now, including high routing performance needs (especially total simultaneous throughput).
With any luck; O/C'ing the RT-AC56U should get even better results in wired routing performance - though I would not be too swayed by this 'feature' nor would I be depending that the router purchased would be able to be over clockable and stable too (that is why I say 'with any luck').
You may ask why the other routers posting higher performance in the charts are seemingly ignored? First on price and the rest on either wireless issues (range, throughput) or simply my unfamiliarity with all the products in the charts.
If price was not a factor the R7000 is the top choice for your routing needs. Even so; I could not recommend Netgear products as the firmware seems to be fixed up to a point and then forgotten about.
Since this will not be the last router you buy and I am assuming you need to buy a new router soon: the RT-AC56U is the most well rounded at this point. With the stability, support, firmware options, hardware components and AC certification to ensure it will still be a viable option for many years to come.
This was not the case a few weeks/months ago; but the latest firmware has made the necessary advances that other manufacturers simply don't do - and; based on past models (the 4 year old RT-N16N, for example) that support will continue to improve this model for a very long time.