Marco,
I have also found that the capability of my 2005 Limited is far better than I was expecting. Last year I placed in the top ten out of 80 cars in a local Mercedes club. Not too bad for rookie than ran 2 of those events with all season tires. Once I upgraded to BFG KDWII they really helped although these tires now seem a little hard for autocross but they are great for the street.
This season I am running 2nd in DS to an experienced driver with a R32. Not likely to beat him but it is fun to set his time as my goal. I even placed the 5 FTD(fast time of day?)in my last event out of 55 cars. Every car that was faster had a dedicated set of tires. So, guess I know what to buy with my tax refund check!
We are down on power to many but the handling and great brakes really make it fun.
Good luck with your season!
Here is a link from last year with some cool autocross pictures.
http://picasaweb.google.com/PrintErr...MBCAAutocross8