I'm definitely not among the experts here, but my feeling is that the 6" seems to be on the low end of desirability and therefore pricing (however, I love my 6"pre model number gun). 3.5" seem to bring the highest premium with 4" right there too. I believe 4" examples to be the scariest, only made for 2 years as I recall. I think 5" guns are probably 3rd on the "highly favored" list. 6.5" guns are not common, either. I'm not sure where the long tubes fall on the scale. As far as a dollar amount, I don't know - as usual, condition is everything, plus value of box, accessories.