I don't know if you've seen my 1:50 on hard mode or not, but during the building fall I was able to make sonic take up the whole screen, it's random when it happens but if it does he falls in about 4.5 seconds instead of 6, which is faster than the building could ever be(6 second fall is about the same as spindashing down the building)
Your 1:50 run is really way better than you think, considering you did without spindashing down the roads,(at the beginning and at the truck) which adds so much luck that it would be impossible to get a flawless run. I just copied your movie exactly and could only do 1:52.
I think you should play it a few times when your bored one day, copying what I did and I guarantee you'd beat 1:50 by quite a bit without much effort, since the luck factor in my movie would probably be 1/20, whereas on yours a perfect run would be 1/1,000,000.