That's correct, 1.5v and 3.3v used different key positions. Cards that supported both were sloted for both keys. There were a few nVidia cards that were officially 2x/4x but didn't support 1.5v because the cardmaker wanted to save some money, but that wouldn't affect anything newer than the GeForce2 for nVidia, nor would it affect ATI or Matrox cards.
<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>