Those BX4’s get high marks and good reviews from everybody who uses them. They are known to be great value for dollar. But you never hear the same of the BX5’s. I can only speculate as to why, but don’t have a definitive answer to that.
Personally, I think it’s too small of an incremental improvement to make any real difference. I would personally save my money if I was you and go to a more significant upgrade for your next pair of binos. Go up 10 ladder rungs instead of 1. Not that I think the BX5’s won’t perform, but where you already own the BX4’s I doubt it’ll be the game changing improvement you’re hoping.