I think it depends on what is the limiting factor in your sight reading. For me, my problem was (is) that I have trouble knowing where the keys are without looking. My teacher suggested just reading fairly difficult things at tempo even if I only hit 5% of the notes. That, I think, is the right response for someone who knows where the keys are, and can read the notes quickly, but is inhibited by fear of not getting it perfect. That approach did not help me at all. Instead I read simple things really slowly without looking at my hands. In fact before that, I just went through all the scales with my eyes closed. That has helped my sight reading a lot. Eventually I'll get to the point where I'm limited by how well my eyes move between bass and treble staves, or by fear of error and I'll have to do something different, maybe even try to read Beethoven sonatas at tempo as my teacher suggest. But not yet.