There will be no one empirical answer that will apply to you. In general, with a hybrid and iron of the same loft, with the longer shaft and the different MOI, the hybrid can be longer.

If you can't get an adequate gapping from iron A to iron B, then adding a hybrid is one way to create adequate gapping. That's why I have a 27 H instead of a 5I, but on occasion, it may be more than 1 club longer than my 6I - hitting it on the proverbial screws. In your case, if you have adequate gapping from 6I to 5I, but not enough distance with a 4I, then you could replace your 4I with a hybrid. With 27-25-23-21-19 hybrids, you would want the hybrid that gives you enough gap from your 5I. It is possible it might be the same loft as your 5I - or not. With different shaft lengths, a 23 hybrid set to 24 degrees may be longer than a 25 hybrid set to 24 degrees. Without regard to loft, you would want a hybrid that is one club longer than your 5I. You'd need to get fit for the correct hybrid to accomplish that.