Steve 90TTZ

I have a 2001 E55 with 92,000km. The manual says to replace after 4 years/ 160000kms whichever come first. When is the best time to replace? Is the 160,000km too optimisitc? I am trying to chase down some mild detonation and was wondering if it could be traced back to my plugs. Are the IK16 a better replacement than factory?

Thanks in advance,
Steve