Stack height on the Duke EPF is 36mm, the Guardian stands 10mm lower at 26mm. The Guardian/Tracker's chasis measures a width of 80mm, I've heard rumors that the Duke EPF's chasis is infact 90mm, which is not 28% wider than the 76mm of previous years. With regards to the mounting pattern, the Guardian/Tracker features 4 screws in the toe and 6 in the heel, compared to the Duke EPF's 4 in the toe and 4 in the heel. The Guardian/Tracker's mounting pattern covers a marginally larger spread than the Duke EPF. The Guardian/Tracker is a heavier binding than the Duke EPF, the Guardian weighs in at 2,960g (6.52lbs) whist the Duke EPF weighs 2,760g (6.08lbs) and 2,790g (6.15lbs) in the small and large sizes respectively. I'm not sure if they are up yet but take a look on TGR and see if you can find the mounting templates for the Guardian and Duke EPF, so you can see some of the differences regarding mounting patterns for yourself.
Hope this helps, feel free to pm if you've got any questions on the above, Joey