After owning 4 Porsche sports cars (993 Targa, 996 C2, 996 C4 Powerkit, 996 Turbo), I decided to go for a Mercedes E55 AMG because I needed the extra space for my wife, the two kids and luggage but I didn't want to give away too much performance. I also liked the E55 design which I think is very nice. After owning the E55 for more than 8 months, after putting a lot of money in it ( by adding 300 kph speed limit raise, limited slip differential, remapped gearbox software, F1 safety car style steering wheel - ALL original AMG stuff installed in Affalterbach), I sold it because I had so many little problems with it, especially regarding electronics.
But also because it lacked personality and "soul", as ridiculous this might sound to you. Driving it was just plain boring.

I went for a Porsche again, the Cayenne Turbo. Now imagine that I'm a guy who gave up E55 performance for a SUV.
And I'm much more happy with the Cayenne Turbo.

So maybe you should think very well about buying a SL55, not only because of the little flaws it might have (however it seems that newer SL55 have much less problems according to my Mercedes mechanic and are highly recommended) but also because of driving fun. Testdrive both, the SL55 and the 996 Turbo and think very well about your final driving decision.