I own a S60R. There has been a lot of discussion about its performance in the Netherlands, where the car has been tested and they found a 0-100kph time of 7,7 seconds for the V70R (mind you the weather was very hot at the time: 30C or 86F).
Later, they re-tested the cars when the weather was normal (it was a december morning, so probably around 10C / 50F), and their retest showed a 0-100 time of 5,6 seconds for the S60R (0,1 faster than factory specs) and 5,8 for the V70R (again 0,1 faster). Not just the weather but the usage of cheaper RON95 gasoline (instead of RON98) caused the difference. The evidence is in Dutch: http://www.swededemon.com/images/ext/autovisier30104.jpg
I can tell you I do believe it will manage 0-100 in 5.7 seconds if you shift at the right time. However you do need the premium fuel for this turbocharged car, something that isn't necessary for a big V8 like the Jag XJR that's described in another comment.
The car is very comfortable to drive and I feel it's powerful enough (especially when revving high).
More of the power discussion can be found here:
I think the car does deserve the 5.7 status though, as you can read in Dutch (run some of the passages at the end through Googles translator if you don't believe me).