I have now used the new UI on and off for about a month, and there are still things that make me use the classic UI more.
Especially two: the inability to adjust connections, making the workflow much of a mess. And the node selection palette.
I strongly suggest changing back to the old tree-based, outlined node selection. It is simply better, and takes up much less space (especially on a smaller laptop – the old one is resizable to boot).
I am sure you will address the speed issue in time (v5 is definitely slower than v4), but the UI prevents me from moving everything to v5 so far.