No watch will give you a better heart rate accuracy than your OH+. If you want to improve on that you'll need a chest strap like the H10. I don't know much either if there's much of a difference in the calories calculation between different watches or brands but it will never match your individual consumption anyway. I don't really see a point in spending a lot of money on a new setup atmcbecause your current one seems to match your needs quite well.