You should take a close look at this thread if you haven’t already. There is a lot of information in there from Roon’s CTO discussing performance considerations with huge libraries. It’s pretty rare that he shares that much information in one thread. Clearly it’s something he’s passionate about.
You are in rarefied air in terms of library size (>800,000 tracks). One key takeaway from Brian’s discussion above is:
“Unfortunately, when a Roon library gets up into the several-hundred-thousand-tracks range, it pushes mono’s memory management infrastructure so hard that bad behavior starts to result. Symptoms might include laggy screen loading, slow focuses/searches, audio dropouts, or other stuff like that. … On all platforms, there is a point where increasing the library size to the extreme results in performance degradation.”
At the time he wrote this it was around 500,000 tracks. You may be at the point where Roon’s limitations run into liabilities. Only you can decide the balance between keeping a library that large and the downsides which come from it.