Makes a huge difference to acceleration, CoG / handling, braking, especially at faster speeds too.
Also on sunroof models - if you strip the sunroof off and rivet a panel over it'll weigh less than a non sunroof model. Reason being is because sunroof models don't have the reinforcements horizontally across the roof.
I've got some sound deadning to strip off the floor plan, electric mirror motors to ditch. Thats probably another 20kg's worth all together. Still got the heater matrix in at the mo though.
Someone else was weighed with similar dramatic weight savings and theirs was 698KG so hoping to be similar! Easy for 230-260bhp per ton with the 3 pot at 160 - 180bhp.