mudguard: I do it once a month for work. I'm going to be in the minority and say it doesn't really bother me.
Same with Nelson to Blenheim and Napier Taupo roads. With big chunks of those dropping to 80kmh it's made very little difference to the actual time it takes.
As for Paengaroa it's almost 20km longer and Google says it takes longer so that seals it for me.
That said I'm never in a rush for work and the less fuel my car uses the better.
85km @ 80kph takes just over an hour
105km @ 100kph takes just over an hour
Thing is, about 1/2 of the road between Rotorua and Whakatane is @60kph so it will take LONGER. And yes on both routes there are places where real speed is lower, but over all the longer route is faster.