Depends what counts as prog metal I guess. Giving it a wider definition and not repeating artists (or thinking too deeply about it):
I've picked mine using these criteria too.
1. Images and Words - Dream Theater
2. Altered State - Tesseract
3. Ghost Reveries - Opeth
4. The Divine Wings of Tragedy - Symphony X
5. Uncivilized - Bad Salad
Probably would have had a Haken album in there, but I usually struggle to pick my favourite