DRPM performance ?

so a couple of weeks ago,
I did a dnf update, and got ~ 19% reduction due to DRPM

that was by far the highest return on the effort Id seen.
previous experience for me was 1-4%.
I should have grabbed a "screenshot" and sent it here.

Whats the "average" experience here ?
are there statistics ?
do *noarch 's do better ?

how often do you see some version of "find/download failed" ?
(it sometimes appears to be a cached-version problem,
particularly if the update is older than a few days)