Hi, I don't know anything about the extentions you're talking about but as soon as I jump to North PowerXT I can't suggest anything else!
Yeah, it's a bit (euphemism?) more expensive than other ones but it really worth the money! Easy to rig, no more efforts and easy in-water adjustments.. I've been using it since october and it's simply great!
For base, north again (I'm not a NS employee, I swear
) : it has a torned 1.2 mm inox base while, as long as I know, the other has a M8 screw with a resistend surface of 6mm.