An update on this issue: we have isolated the things that Dorico 4 is doing differently than Dorico 3.5 in this regard, and in an initial test with BBC SO we have got the response time down to more or less the same as Dorico 3.5. The change will have to go through testing and so on, but there’s reason for optimism that this should be resolved in the next update.
If anyone hasn’t downloaded D4.1.1 yet, give it a try! The above BBCSO Pro test went from over 27 seconds in 4.1 to under 1 second in 4.1.1 for me.
Just tested this on my project - such a quality-of-life improvement!
Great work, Dorico team! Thank you!