You will get better results on Startpage because they feed unfiltered google results.
It's actually a good way of detecting whether or not you have a google penalty as opposed to just a site that the algorithm just doesn't like.
If your position is the same on both then google just has no more love for you (if you are deep in results). Whereas if you are at maybe position 150 on Startpage but position 400 on google for the same term -- the difference is your over-optimization whack-down.
It's just IMHO of course, I don't know that with 100% certainty but the indicators are strong enough to consider it for your own situation, hence worth mentioning here.