Durano Plus tyres versus GP5000s!
I have ridden both tyres, and rate them very highly, but for me they are for very different situations.
The Duranos are fairly heavy and have a whacking great thick foamy layer to try and protect the tube, generating a fair amount of rolling resistance.
I used mine in the past for commuting and as a winter tyre - only one breach which was a ginormous thorn.
GP5000s are my summer tyres, and they roll really well, have low rolling resistance, and are much lighter.
I carried out a test on a local 80km loop I ride regularly on consecutive Sundays, same bike, one Sunday with 25mm Duranos, one week with 25mm (I've since migrated to 28s) GP5000s, and the unscientific result was a 3.2kmh speed difference, so I do not doubt your own findings one bit.
Fwiw, when I upgraded I went to Spokesman wheels, and he built me a set of wheels exactly to budget and as light as we could go within reason, based on the bike it was for - delighted with them.