Sorry pal, Stan Lee said nothing about Thor's strength only that Hulk is mortal and Thor is a god. His only reference to strength in that comment was actually about the Hulk. He also had said, it depends on the author in any conflict because they are god and Stan hasn't written Marvel comics in decaces and the weight of all the creators through the long history have clearly indicated Hulk is the strongest one there is. World War Hulk and World War Hulks showcased this, as did Hulk smashes the Avengers mini recently but go back decades to Secret Wars.The Hulk supported two miles and 150,000,000,000 tons of rock to save everyone. Thor's mightest blows from the surface were only heard as faint taps from the depths where everyone else stood under the Hulk's labors.
I definitely accept Stan's premise that Thor is a god and immortal and that imbues him with a number of abilities beyond strength.
Thor is probably stronger than the Grey Hulk but that's it.