My experience has been that total rotating assembly weight is as important as how you choose to strengthen the block. The next motor I get is going to have aluminum rods, the lightest piston I can come up with and a low deck race block from KB. My last choice would be what i have now, a four bolt Megablock with a 2432 bob weight. I don't like the idea of a conversion four bolt kit simply based on the fact that I have hurt a better four bolt combo, the factory four bolt race block.
The best choice for a stock type 440 block IMHO would get a set of aluminum caps, and I would spend as much or more money on light parts to keep the bob weight as low as possible.