Latest issue of Wheels compares the HSV W427 and Mercedes-Benz CLS63 AMG.
AMG is quicker to 100 (4.7s for AMG and 4.9s for HSV), but HSV has faster rolling start times (for the 80-120km/h run in third, times were 3.1s for HSV & 3.2s for AMG).
AMG costs $269,675 compared to $155,500 for the HSV. Wheels gives both cars 4 1/2 stars out of 5, and says if it were their dollars down they'd choose the HSV.