I also went from BAM200 to powerstage 700.
My main reason was that when I wanted to push some dB's for lead the BAM could not handle it and it hit the ceiling (the volume even dropped due to it's saturation). I need to keep up with a 100W tuba amp so I need a lot of headroom ... The SD can keep up with ease !
For "normal" loudness the BAM did fine, the SD's 700 W is a walk in the park. Also the input signal strenght is important, never knew (and still don't) have an idea how hot the input should be (the BAM did show the input signal with the colour of the LED, the SD does not I suppose)
PS : in a recent rig rundown from Dave Mustaine they aslo have the powerstage 700's in their racks to power some onstage cabinets (besides the in-ears)