How important is it to focus on performance now our connections are faster than ever?
Performance is still incredibly important as people are increasingly using mobile devices. It'll take a while until mobile connections catch up with the speed of wired connections, and many users globally are on slower infrastructure.
How do you convince upper management to care about performance?
Show Very Important People videos from WebPagetest of how long your site takes to load on mobile connections, and use test locations around the world to help them feel what your users are experiencing. Compare videos of your competitors' sites next to a video of your site loading; pride is a powerful tool!
What matters more: total load time, or perceived performance?
Perceived performance will have an enormous effect on the overall user experience, and is worth optimizing. Fix scrolling jank, and make sure the primary action for a page is interactive immediately upon page load.