Pinochet secured his power by engaging in widespread, systematic mass murder and human rights violations; Allende did not. It is simply not valid to draw a parallel between the two in terms of "crimes against humanity."
Your argument for Allende's campaign of "torture and murder" is based on a series of fallacious appeals to authority. You can't use the contemporary accusations of opposition figures like Aylwin and Frei as sufficient evidence. All you've proven with your response to Mr. Letelier is that Allende's opposition opposed him. For what it's worth, Aylwin was grossly exaggerating Allende's military power (armed groups in the rural areas were weak, and largely outside of Allende's control), and I don't see how Frei's call for a military coup supports your argument. Again, it tells us about the polarization of the time, but what of Allende's supposed torture and murder? Pinochet's brutality, on the other hand, is beyond dispute.
And do you really believe, based on the testimony of a single disillusioned guerilla, that Allende and co. were planning to export violent revolution, in the Western Hemisphere, during the Cold War, with the US already hostile to them? It doesn't take Henry Kissinger to figure out that's suicidal. Again, the evidence provided is insufficient to support your claim. One accusation of a supposed future conspiracy does not put Allende any closer to the level of Pinochet.
Finally, your assertion that "whereas Allende left Chile in shambles, Pinochet—unlike any other dictator who comes readily to mind—left his country much better off for his tenure" is a gross oversimplification. Could you make a serious argument for this? Yes, it's a complex topic. Can you do it in one sentence? No.
Of course it's true that Allende's administration was an economic and political disaster after the first year. But you can't just ignore Pinochet's brutality when declaring that he made Chile a better place. You're discounting the lasting effects on Chilean society, politics, culture, and victims' families. Even if, for the sake of argument, you leave that aside and consider only economics, the situation is not that clear-cut. Pinochet did effect a large increase in GDP. But that's only one indicator. Under Pinochet, real wages remained stagnant for almost twenty years, and unemployment and poverty skyrocketed. These situations only improved when Pinochet loosened his grip and allowed Aylwin to claw back the most extreme neoliberal policies. So Pinochet and the Chicago Boys facilitated economic growth; but I think if you asked the average worker, peasant, or Mapuche, they'd have a different take on Pinochet's economic policy.
If you want to make a serious historical comparison here, you need to find some sources that are more balanced and credible than the accusations of Allende's opposition. I suggest Collier and Sater's "A History of Chile," as well as the following article from The Economist: http://www.economist.com/node/184063