That's exactly what happened with me 3 days ago. I had purposely avoided using Gillette razors until then. I'd played exclusively with Merkur and EJ. Then I decided to try finally a Slim and SA with the three blades (Sharks, Astra and Derby) which I didn't like until then. I started with the Adjustables on #7, half face for each razor, switching the three blades. And all of a sudden, as you said, on #5, the magic happened with the Slim. It just felt it like something snapped. It worked flawlessly with all three blades. I just couldn't believe the difference it made. It felt so different and the feedback was great. Maybe it was the closest shave I remember.
-= Boris =- The man thinks, the horse thinks, the badger thinks, the boar thinks. The fish doesn't think, the fish is mute, expressionless. The fish doesn't think because the fish knows everything.