I looked at getting one of these before I got my VXR8. My VXR8 is running at 472bhp at the moment and can keep up with C63's no problem but I haven't owned one so can't say much but I think my car is pretty similar even though I would still say the C63 is in another league on quality etc. I get 6mpg driving normal around town, 14mpg if I'm being extremely careful with fuel, 15-19mpg when down a long motorway run driving normal & have seen figures of upto 25mpg when being careful on motorway journeys. I use mine through winter no problem, just put it into manual mode in snow and ice but it's not the same as actually driving in a manual of course. When it's wet or snowy the back end does kick out sometimes on normal driving but TC kicks in n soon stops it so I've never had any problems or near misses.
One thing that I wanted mainly when i bought mine was a fast car but for decent money. It's standard figures are 412bhp, 0-62 in 4.9s, top speed is 155mph limited. The current figures are 472bhp, 1/4 mile in 13.8s and approximately 4.6 for 0-62 and over 175mph. To buy mine would cost £16,500 now and is pretty cheap to service compared to the BMW n Merc equivalents.
I've personally seen less VXR8's upto now than GTR's, M5's or C63's but that's what I prefer, the LESS common cars, even though 2 of the above aren't exactly common in my eyes.
Just my opinions & experiences :)