I think that you were fooled by the news coverage. It's only on non-divided highways that the new restriction applies, and there was already a restriction to speed limit + 5mph on such roads. On divided highways, you can set any speed up to 90mph.

Here's an accurate article, which (alas) still has an inaccurate headline: https://electrek.co/2016/12/22/tesla-autopilot-speed-limits/