You note that CEA and 80K don’t seem to be struggling for funds.
What makes you say that? (Not saying I don’t agree, just am unsure)
Unfortunately I do not have a single easily quotable source for this. Furthermore it is not always clear cut—funding needs change with time and additional funding might mean an ability to start extra projects (like EA Grants). However, unlike Rethink Charity or Charity Science Health, there is not a clear project that I can point to that will not get funded if CEA 80K do not get more funding this year.
If you are donating in the region of £10k+ and are concerned that the larger EA orgs have less need for funding, I would say get in touch with them. They are generally happy to talk to donors in person and give more detailed answers (and my comment on this matter has been shaped by talking to people who have done this).