Replacing Linksys e4200 with RT-AC66U enough or should I get something better

[ex313]

We recently upgraded to a 60mb cable service and the E4200 running tomato is not keeping up with all out clients, plus I want to go to an 802.11ac router. We have about 15 clients on at any given time. Don't really need QOS with the bandwidth we have available.
Was going to get an RT-AC66U and run Merlin's firmware on it - do I need more for what we have in the house?

 

[microchip]

the original ac66u is pretty old, make sure to get the B1 revision which is similar to the ac68u

 

[ex313]

Is this the same as the B1 AC66u?
https://www.asus.com/us/Networking/RT-AC1750/overview/

what about a jump to the AC1900p?