The Spyder can make things worse, if your projector is performing properly in the first place. Autocal, when it works well, has some advantages over manual calibration as it works at a lower level so calibrating one gamma level (e.g., 2.2) will "fix" all gamma levels.Thanks, here is manual -3 iris, custom 2.4 gamma. Differntly off. If the meters are that far apart (dE's up to 13) is the spyder helping or just ruining everything?
However, any calibration results can only be as good as the meter used for calibration. In the first post (by Manni) there are a few links describing how to correct for errors in the Spyder.
BTW, it's a common misconception that RGB Gain only affects the upper end. It applies to the entire range proportionately. Here's an example showing the effect of changing only the RGB gains: