I used to experience a very short delay of a sec or two occasionally when scrolling or manipulating pdf files (such as taking notes or highlighting text), with A&R pane on, in an index group of approx. 1000 items in DT3b1 to DT3b3 (more in b1 and much less in b3). It seems that these delays are pretty much all gone in DT3b4. Just FYI and thanks for the optimisation!
Thanks for the nice feedback! Beta 4 saves now modified PDFs asynchronously in the background, therefore you shouldn’t notice any delays anymore usually.