Nara to Kumano by car during GW

I'm wondering about the feasibility of driving from the Kashihara area to Hongu Taisha and Nachi Taisha. Google maps says about 2.5 hours to Hongu, but the bus takes six, so I'm slightly worried how long the drive will actually take.

Also, if going during Golden week, will roads in the Kumano area be impossibly crowded?

I drove round there a couple of years' ago during GW and was surprised at how reasonable the traffic was.

However, google driving time estimates are TOTALLY unreliable! My rule of thumb is to add at least another 50% onto whatever time it tells you to give you an accurate idea of how long a drive is likely to be.

As an example, a trip I did last weekend that was supposed to take just over 2 hours according to google maps took over 3.5 hours going there and over 3 hours coming back...