I agree, the difference is in the core. I have always liked the Activator series of cover stocks. I drilled my Pink/Purple Karma pin up at 4.5" from my PAP. The reason is I have fond the Activator+ to read the mids almost too well. I wanted to get the ball a little further down the lane with plenty of pop on the back.
From what I see I put the Karma right between the Absolute Inferno and the Vapor zone in terms of strength and angle off the breakpoint.