Also depends on the pilots that fly them!
Alitalia's B767 fleet was introduced as a "low-cost" fleet from a crew perspective - many of them were initially crewed by Ansett crews (VH- registered) then by Air 2000 crews, followed by Monarch crews (G- registered) before they were placed on the Italian register (I-)
I suspect the Irish registered aircraft may be operated differently from the rest of the fleet for a reason other than who owns them... Alitalia's current EI
- registered B767s are leased from GECAS, which is of course American.
Registering some aircraft in Ireland will probably be because there is a financial advantage to do so, or possibly an operational one...