XP2 certainly has excellent exposure latitude, especially toward overexposure, although there is noticeable deterioration in image quality with moderately large errors. I have less experience with HP-5, although I have some and I have done several sensitometry experiments with it. My conclusion is that HP5 also has excellent latitude, but it behaves a bit differently. You should have a good hit rate using the sunny 16 rule with HP-5. A light meter is a good investment in any case.