The higher temperature ones aren't as insulated but feel like they are heavier and stronger than mine, mine are the lightest, and at the time didn't care about anything higher than ~2000F.
KaoWool is one thing I don't know anything about, but;) like another poster said I suspect it to be a better insulator than my bricks... but not as much as he described, I believe he was comparing kaowool to regular fireplace brick.
There's sure enough one way to find out tho ;) a regular fire brick is pretty much the same temp front to back... when it comes to picking one up with your bare hand. ;)
The type of bricks I have are exactly the same material as what is in the electric-ceramics-firing-kilns. You could go by a ceramics shop and ask about it and see it and feel it first hand.
I did that early on and I was given an old kiln. ;) It was in really bad shape, left outside for years, they just never got around to hauling it to the dump... salvaged some bricks from it and the controller. I took then some ceramic shelves/plates(?) for stacking ceramics for firing in return.
My bricks look and feel and "sound" like cream-colored stryofoam.
The higher temp bricks are more glassy looking and heavier.
Alvin in AZ