It's been "temporary" for 6 months now though... May release with 75 limit, bumped to 80 mph in June... hasn't improved since.
I've seen no evidence it has anything to do with HW3, and more likely has to do with the main forward camera having less range than radar does.... (150m vs 160m in this case).
The ARS410 realized a broad field of view by two independent scans in conjunction with the high range functions.
www.continental-automotive.com
170 meters of range on the radar in AP2.5 cars.
Vs 150 meters of range on the front main cam.
That's about 558 feet for radar, vs about 492 feet for vision...a difference of about 66 feet.
Braking from 90 mph vs 80 mph takes roughly 88 feet longer (given all else being equal), so right ballpark at least to explain the difference.