Riding the shoulder is illegal in New Zealand, but lane spliting is legal.
I do it daily to travel to and from work, it's one of the primary reasons I got my bike in the first place... To cut travel time. Gone from 1hr to 25 min.
The motorways are typically 80kph and I'll happily lane split to that speed when thr traffic is doing 20-30kph or less than the limit.
Most people will move to give you space so its easy, but I always ride with my foot on the rear brake and fingers on the brake and clutch ready to stop quickly should I need to.