The longer duration cam should run higher in the RPM range from my also limited understanding. One thing to check, the stock Magnum valvetrain seems to be good to about .5" lift. Upgrades to springs, seals, studs ect. are probably needed with either of those two cams. The .566 lift version looks like its a very fast rate cam... I'd make sure the stock hydraulic lifters can handle it with required springs.