This seems much more like a style of driving decision than a HP numbers decision. The SR wins when it comes to higher numbers. I've been doing a little researching and this is a dyno of a stock SR
http://www.conopium.com/cars/dyno1.jpg
The KA WILL spool faster, and could theoretically hit higher boost numbers, BUT we're not talking about normal ranges here. By normal I mean anything less than 25 psi.
The overally effectiveness of the engine is a moot point. The SR handles load better, and is more efficient. When the exact same turbo is stuck onto both engines things start to change a little bit. If you get an SR you shouldn't be using the same turbo as a KA would. Higher CFM is determined by the intake side of the turbo, while spooling speed is determined by the hotside.
If there aren't many SR owners running a twin turbo setup with something around the 11B size then I'm going to disregard the cars entirely. Logically that is how you will make the most effective use of the engine itself.
Price ignored, the SR is a better engine. The KA is apparently cheaper, and quicker to mod but doesn't respond to mods as well.
For Auto X, the KA would be a smarter engine due to spooling speed and a smaller low end torque, for drag the SR wins. A properly modded SR should beat a properly modded KA.
I've seen little evidence of weak ringlands.