Re: AGM-type battery vs. standard lead-acid. The original lead-acid battery in my 2004 545i lasted 7 years, thru 2011. When it died last year, the dealer wanted to sell me an AGM-type battery, saying this is all they carry any more. This is when I found an exact match for the original lead-acid at Batteries Plus. This is the story I was relating above. The battery in my 2009 M6 is still going strong, but it appears that BMW has fitted an AGM-type in these later cars. I cannot say what type of battery is fitted in your 2007 M6, but if it's the standard lead-acid style, not AGM, I do not see any reason an exact match will not work, just as your original battery did. If you car came with an AGM-type, then I would go with that instead.
2009 M6 Coupe, SMG
2004 545i Sport, 6 MT (Sold)