I recently updated some old work from 5.6 to 2019 with a pitstop in 2018. There's slow but consistent slippage in terms of editor speed and responsiveness during common and frequent operations: playmode enter/pause, editor panel display, object selection updates, panel resizes, etc. I wanted to just raise some awareness, if you use 5.6 then 2019, the responsiveness and general feel has a noticeable decline. I don't think this is any one thing, but instead just the slow accumulation of performance cost from additional features or logic. I hope someone at UT keeps an eye on this stuff going forward.