What optimizations still need to be made to Transmission, other than async nonblocking disk IO, to make it the most efficient torrent client out there?

[Pentaphon]

Again, this is besides the obvious request for async nonblocking disk IO #2462 so please don't mention that here since many people want this and it is a longstanding, long term goal for the project.

Other than the above, what optimizations still need to be made, if any, to make Transmission the most efficient torrent client out there?

I'm hoping this thread will result in new ideas (or overlooked solutions) that have yet to be proposed in the issues.