I wouldn't buy an M5 either. If I wanted that size I'd be in something Italian anyway.....even if it couldn't keep up I'd smile smugly knowing I'm not in a hotted up rep mobile favoured by chavs and drug dealers.
I prefer the looks to the M5 - maybe that is reason enough for its existence. If I had the money I would definitely put it on my list, which surprises me because I don't normally like BMWs. 4 door saloons which don't pander to the passengers are very appealing to me.
There again, I am of a "certain age".