I'm having similar problems with my V5, by the looks of it the traction control is getting over enthusiastic. If I turn it off I lose all flat spots and can accelerate as much as I need to.
Of course, I don't know whether yours has traction control, but if it does, try switching it off.
The other thing I've noticed (again with my V5 but might apply to you) is that it really didn't like supermarket unleaded petrol, it caused a distinct lag at the bottom of the rev range. A switch to brand name super sorted it.