If BR 4 had flooded at the same rate as the rest-
Titanic would have sunk with less then a bow-down attitude. That being the case, the water plane would have been longer and consequently - the possibility of her main strength members breaking less possible. This would have been because less of the hull would have been unsupported by the sea. i.e. - she may have sunk intact.
For what it is worth , a hole in the bottom shell plating would not have flooded BR4.
Titanic was virtually flat bottomed.
In way of Boiler Room 4, the bottom was double. The space between the outer and inner bottom was about 4' 6" deep and and transverse framed by deep floors at 3 ft intervals. If as suggested , ice acted upward on the outer bottom, it would have done so long before it was directly under Boiler Room 4.
If for some reason it did not do so until it was under BR 4, it would simply have sprung a few rivets in the seams between the frames and water would have entered the WT Double Bottom space below the inner bottom.
On the other hand, the water seen in BR4 must have gained access to the space between the inner bottom and the boiler room floor plates. It could only do so above the margin plate of the bilges, through the ship side or by over-topping WT bulkhead "F". Excuse sketch:
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