One important aspect of uploads is that they can (presumably) be easily copied - this is enough for them to have a huge economic impact even if they only run at normal human speed. If you have one upload that is willing and able to do a job, suddenly you have as many as you need, and can displace all human workers in that job (at least once the hardware gets cheap enough).
This assumes that uploaded people would agree to being copied or that the world turned so dystopian that no one would ask them for permission. I for one wouldn't want several instances of me running around.
Master version on gwern.net