I am currently on a D3 ARC-S. I came from a D3 Z7st and a D3 X7. (Was alternating between those two for about 2 1/2 years before I switched.)
The ARC-S rides like a typical D3 ski, just a bit more "refined". So no surprises here. It is very predictable and forgiving, turns incredibly smooth and is still fast across the wakes. It is/was actually the first ski that allowed me to make up time & even angle between the buoys @ 55k.
I have no experience with Radar skis though, but as a D3 skier, the ARC is definitely a ski you will like!