The factory does set the limiter at 158 mph. It's clear by the acceleration and RPM that the little cars stand a chance at touching 170 mph. I don't think they have the wheaties to do much more, but that number should be possible.
We know that Mercedes can remove speed limiters on their vehicles via programming. That's evident by the performance packages available on various AMG models.
An SL55 has a top speed limited to 155 mph. An SL55 with the 030 performance package has a top speed limited to 186 mph.
The SLK55 with the performance package has it's limiter moved to 172 mph which is more than enough for such a short wheelbase.

It may be possible to remove our limiter also. One of my techs mentioned last night that it was stored in the ME. We might get into it to see if it can be accessed.

Yes, I'll still sell the car. Needs outweigh wants. Besides, I've got a little black car with twice the power of the SRT. It's getting a suspension upgrade this summer so it will handle in a similar fashion too.