P-Pump 24 Valve Cummins are used in the most high end applications. Look at all the drag cars. They P-Pump 24 Valves for a reason. Depending what kind of tools/shop you have, it might be easier to swap a 24v for a 12v. But a P7100 on a 24 Valve will have much better results.
Standard Outputs also have advantages over a 12 Valve like lower compression and no offset injection.
Also the blocks are suppose to be stronger than 12 valves. The 53 Blocks had issues, obviously, but that had nothing to do with power. Supposedly some of the 2001-2002 blocks were the strongest made, but I also heard some of the Common Rails had the best blocks too. It wouldn't surprise me if the 12 Valve blocks were weaker.
But me I really could care less what block is the best. I'll never build a engine so powerful that the block strength is a issue. All the blocks will last 4 Million miles with stock power.