While I never personally compared the 2 in EXACTLY the same hull, I have read many, many articles over the years on that subject. Trailer Boats magazine often did "shootouts" comparing different powerplants on equal boats provided by the manufacturers..
That said, my gut feeling is that if the hull were truly the same, any difference would be because of a weight difference....with the heavier boat riding better. However, as just pointed out if you added one more fat person on the OB version, the 2 would then be the same weight. Regardless, I doubt that 300# more or less would be significant.
The 150 OB vs. 4.5 I/O weight comparison above was interesting. Our most recent boat purchase came with either of those 2 powerplants. In the case of SeaRay, the dry weight of the OB version was actually 75# HEAVIER than the I/O. The hulls that are in the water are the same. I would guess that since the OB is cantilevered out to the end of the swim platform, the added stringers more than make up for the lighter weight engine.