Our systems seem to chug along fine with the recent upgrades installed. With the full switch to SSDs came the right opportunity to switch database engines too (we went from mongo's old MMAP to the newer WiredTiger).
This means huge performance boosts for lots of common queries, and in the process the database size was reduced by 90G. (Although data is saved more efficiently, most of it was empty reserved space anyway.)
I hear you, this doesn't automatically mean all the sources of your performance complains have vanished, but at least it solved the charts hanging forever when making a wrong swipe. Next steps to make the thing more responsive will be to reduce the size of data that is sent to the browser. Also initial page loads will improve with the right js packing.
On the topic of user experience, work was started on a layout revamp. This is mainly done by removing clutter and making the charts easier on the eye. Also, I want to integrate the way post indicators are shown (the little blue and green charts when you click a news item, showing the absolute and relative post score over time). Things are still experimental, so it will take some time before it lands in your browser, but it may have something to do with streamgraphs.