it's a simple way to compare whether the delta RPM thing is saving you any time. If that speed is faster than your download speed, it is...
Do you mean there is a parameter a user can employ to control the balance between network and processor resources for an update? I surmised the object of the delta strategy was primarily to reduce data traffic at the servers, with a secondary benefit of faster delivery to users with small network bandwidth.
I have found the rebuild speeds displayed on my F12 test system one-quarter to one-tenth of my network bandwidth. This has not been onerous, but certainly time would be saved if I could say "Do not use delta rpms." to yum.
Recent experience has delivered the worst of both worlds: about half the delta rpms fail integrity checks, and complete copies of those files have to be downloaded after the delta rebuild failures. An earlier post to this list explained a format change causes these failures, and they will abate as packages are rebuilt.