With the 20V wired so it will rev-cut at the right spot, it will speed cut at 180km/h. So will the GZE if it's wired as it should be from factory. if you cut the VSS input to the ECU's they will both do a lot more than 180, but the 20V will rev-cut in the mid 7K range instead of over 8K.
I have a blacktop 20V in an ae92, and a MAP GZE in an ae92 and IMO the GZE is a lot more fun to drive round day to day.
There's way too many factors that come into insurance costs, so the only way to get a real figure for that is to ring around the insurance companies. There's not a hell of a lot you can do to a 20V to make it go harder without spending a fair amount of money, with the money you spend you could have paid for the insurance on a GZE...