I'm trying to figure out why there is such a substantial price difference between these two models when as far as I can tell from the spec sheets they are absolutely identical except one is aluminun alloy/stainless and the other is aluminum alloy/carbon steel. I always thought stainless was more expensive than carbon steel but I guess I'm wrong as far as these models go. The 442 goes for over $100 more generally than the 642. Is there some other difference I'm mssing? They both weigh the same and are identical in all other respects except for material. Thanks. Fleiger