In the overall Battle of Memphis I doubt they would have changed the outcome given given the poor preformance of the rest of the Confederate Fleet and general command failure.

The Maurepas would certainly not have been of much use. The Ponchartrain however certainly could have been a match for anything in the Union Fleet except for the City class ironclads. In close combat it may well have stood up to them. She was as well armed as the City class Ironclads and with 20 inch Oak Casemates may have been the equal to the City class railroad rail armor if you have ever looked at the USS Cairo down at Vicksburg.