The vocals... you can't define as either power or progressive, but the lyrics are much more similar to power metal than they are to progressive.
Barlow is much more Prog. than he was power. He mixed it up quite a bit, but overall, progressive.
Overall, you bring up good points, but Iced Earth really does mix it up very well between progressive and power...fuck, just listen to Dante's Inferno...vocally and musically, this is progressive at it's best! Some of the new stuff from Glorious Burden (the reckoning) is pretty technical.
Iced Earth is very diverse and I can see where you're coming from, but I wouldn't call them Power Metal and leave it at that. They are pretty progressive as well. But who cares? All that matterts is that they fuckin' rule.

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