Originally Posted by
Mimi05SRT6
IK20 would be for the stock SRT-6. The IK22's are only 1 step colder.

That's weird, every single site I have gone too say's IK16 for stock SRT-6 as well as the CLK320...
Here, even Denso say's IK16 are stock!!!
Denso automotive parts available online at DensoProducts.com