If you experience a misfire at high revs and full bore, get it sorted immediately. My CLS is stock, but when I bought it I had the intercooler coolant pump changed at once as a precaution; once bitten, twice shy...
(Short story: Intermittent intercooler coolant pump fault - random misfire at full chat high revs, EML illuminates, switch off then on again and all is normal - no fault codes - new plugs, coils - still occurs, but car fine nearly all the time - sudden loud rattle on startup - bent conrods, one scored bore - £11k bill. I could afford it, but I'd rather not have had to...
See this thread:
It's Not A Good Sign When... | General Discussion for the full story if you're interested.)