Hey, I run EA Funds (so feel well placed to answer your question).

We currently don’t use donor money to cover our operational costs so in some sense we are very efficient.

Of course, making a donation does create some costs for us (as our team needs to work out where to send your money) but I think overall our team is selected to try and make this decision well so outsourcing the cognitive labour of working out where your money is better spent is plausibly worthwhile (and I expect to see economies of scale when doing this ). To be clear we would be very excited about receiving your donation (and that would be my recommendation).

I also think that the performance of the funds are higher than that of the median org we fund as we are pretty hits based in our approach, and we have access to more information than I expect our donors to.

Not exactly about efficiency, but in terms of impact I suspect that individual small donors would have more of an impact through directly funding small projects that larger funders such as EA funds can't or wont fund due to reasons such as the lack of capacity to evaluate them.
 

More reading on this here.

https://forum.effectivealtruism.org/posts/oHcRQsiDM9D76aENu/a-red-team-against-the-impact-of-small-donations