I also have that AC66u but the CPU seems pretty much more than enough. I tried using DD-WRT for so I can use more of that CPU and RAM but the Wi-Fi AC speeds seems to not working properly, giving me low data rates. Besides, the router really feels warm with many devices connected to it.
More powerful CPU could be useful for multiple VPN connections and Wave 2 of AC, the one with multi-user mimo.
At Tom's Hardware, you are sure to find a few typo's. Obviously its suppose to be GHz. A processor running at the speed of an Apple II on today's manufacturing process would be smaller than the solder used to mount it.
To me nostalgia will not have me overcome the fact its a Belkin company. The only non-cheap crap I have gotten from Belkin was the n52te. Its cheap, but not crap.