Predicting is the easy part, but proving it is another story. As of now, i don't think that a site can predict bitcoin price changes accurately, even in long term. This is due to bitcoin's instability and acceptability. Yes many already accepted bitcoin but let us not neglect others who do not. We do not know exactly how others think about bitcoin. And as of now, other organizations may be having debates about its acceptance, even how to deal with BTC. If we are talking about sites that is able to predict long term price changes of bitcoin with a percentage of 75, I cannot guarantee if there is any. But i hope in the near future, BTC value changes will be predicted accurately. ~Cheers