There's a very real chance you'd only get 2-3 good years out of Dunn. If you feel like Gonzalez can be an elite hitter for at least 4 years of the deal, I think you do it. At that point, you can trade him for value or keep him if you feel that he can keep producing. Personally, if he wants 8 years or if the Padres want some silly deal like Wells/Cashner/Vitters/Lee, I might balk and go after Dunn instead. If he's looking at 4-6 years at mega money, however, I think he's worth more than Dunn, even giving up good prospects.