Up to about 650 hp both will work fine. The 400 block is a bit stronger in places and if I was going over 650 hp I would use the 400 block if I was gong to stay with the stock block but much more hp and your getting into aftermarket block territory. Myself my 493 is a 440 block as I wanted to have the selection of the 440 intakes. As for reving once you stroke it then it will depend on the stroke you use as to how quick it revs. In stock foorm the 400 revs faster then the 440 do to its short stroke but when stroked it may not if you put a long enough stroke in it. Ron