It would be one hell of an achievement even if the new F90 M5 is just 1kg's lighter than the F10 M5.
1 kg off would not be much of an achievement imo, considering the only thing that will be added is AWD, and that sure as hell is not going to weigh that much. The F10 M5 was around 1950 kg EU, I expect the G30 M5 to be well below 1900 kg EU, considering the weight difference between a comparable F10 and G30....
For reference, the E63 S AMG weighs 1955 kg EU. So the M5 will be below 1900 kg EU. The weight difference will be 50 kg in favor of the M5 at the very least.
Sub 3.5s I believe as per the earlier post. So it means it is below 3.5s.
And I'd like to add that (obviously) 0-60 MPH is not equal to 0-100 km/h. You generally have to add 0.2 seconds to the 0-60 MPH time to get to the km/h time.