Here's my view, as long as you drive sensibly within the law and by the highway code you should be fine, also if you've been learning to drive with a company that taught you in a smaller manual car then you need have good spatial awareness when moving from such a small car to something so big and nice.
After saying all that, sure the CLS may have ~300bhp but just don't boot it around corners and accelerate stupidly, most cars can be driven too fast and over the speed limit, it's just about self control.
Also remember one thing, just because it's fast doesn't mean it can defy the laws of physics, I had a bad crash once because I was overtaking and the guy coming towards me was coming speeding, I had a bmw 325i sport auto, the auto box didn't do what I expected, or put simply the car wasn't fast enough to get out of the way, needless to say, the guy coming towards me died because he didn't have back brakes, wasn't wearing a seatbelt and was doing 95mph on a straight B road. I got done for it eventough I felt my judgement to overtake at the time was correct, I was barely doing 60mph when overtaking... 60 + 95 = 155mph towards each other.
So what I'm trying to say is, it's not just about speed or being too fast, it's about sensing space and time and that only comes with experience.