I recently drove SH6 over the Whangamoas. Most areas that were once 100 are now 80 or lower (except the closest part near Blenheim). I was towing a trailer, and it did not add any appreciable time to the trip, but made the whole drive much less stressful. No more Utes up my arse because how dare I not do the full 100 on the windy as fuck road. So from my personal experience I like the change.
It also helps that 80 is right around the most fuel efficient speed, which is nice now that petrol is $3+