IMO the answer is: it is a mixed bag, there is no super clear winner here!
They are all clearly 1-10 second "burst" amplifiers, they need to recharge their capacitors and cool their heat sinks in between these bursts.
But overall the K10 has my vote, because it has 10% more efficiency, double the power density, and the limiter doesn't choke as much after 2 minutes.
The IT8K and K10 burst some impressive numbers. In bridge mode they will all deliver north of 10,000watts for a few hundred miliseconds; and hold something "near" that for ~10 seconds. More than enough to blow up any subwoofer.
240v/30amp almost sounds "required" if pushing hard, or at least a 15-20.
(Double for 120v)
I'm sure the FP14K is up in that range too...
Does anyone have graphs of the FP14k?
(It's almost unfair to compare these two against a 6.4k; a bit beyond its league.)
I run my IT8000 in dual 1-ohm and it seems fine with this.
I have never experienced this power "limiting" with it... and I've played bass tunes on it for so long (like 6 hours non-stop) that my LMS-18 started overheating.
I had to turn it down because of the LMS, not the amp. It was mostly half excursion and whole time too. Never clipped or overheated once during this; it would have easily kept on going to the LMS's demise long-term.
If this is true, a K20 would have killed a pair of LMS's without even giving it a second thought.
One day I have to try me a FP14k clone just to see what she can do... because if you never try, you never know.