Play Services 13.2.78 Ultima Version !!top!! — Google

For Android 5.0 and 5.1 devices, 13.2.78 represented the peak of performance before later versions (13.2.80 and 13.2.90) introduced heavier background processes.

To understand why this version is considered “ultima” by many, here is a direct comparison to a modern Play Services version (e.g., 24.xx.x): google play services 13.2.78 ultima version

Many users refer to this as the "ultima version" because it was one of the last broad-compatibility updates before Google began deprecating older Android APIs. Google Play services - Apps on Google Play For Android 5