Many moons ago I was a government employee and they used to give me a new XF van every 9 months or so when they got to 40,000 KM
I had a leaded XF followed by one of the first unleaded ones.
Both vans were identical ie same diff ratios and 3 speed column shift manuals.
The leaded van would pull 145 at the top of Lidster hill near Orange if you hit the bottom @160
The unleaded van and the next couple of vans I had would be flat out at 100 at the top of the hill. XE vans had similar performance to the leaded XF but they were autos.
I would certainly say that there was a loss of power when unleaded was introduced.
Ah the things we do when we are young and stupid....