I have a few bikes .... I ride with the same effort and the same wind conditions
on my Condor vintage steel bike with Schwalbe Durano plus, I average just over 27 km/hr for a 40 km stretch (little or no wind)
on my Surly Long Haul Trucker with wider tyres, I average very similar (just slightly slower)
On my carbon Giant TCR with Continental Grand Prix II tyres, I am 6 km/hr faster