When the knock sensors detect noise, two things happen: The timing is retarded and fuel flow increased to cool off the cylinder.
My theory is that both of these things happened at over 5000rpm and at full throttle. The ECU retarded timing AND the fuel flow increased, causing raw gasoline to get to the CAT. The front and rear O2 sensors sensed the workload and the apparent CAT inefficiency and threw the code.

You should be OK. Just remember, 87Octane will lower your mpg even at normal driving range. 89octane works OK, but not over 5K rpm. 91 octane is what your engine wants for performance.

I tend to use 89octane on the flat Midwest Interstates and 91octane around the suburbs where I am always accellerating.

Klaus
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I still miss my 164 and my 854T. Just driving a V70R :)