I have a p3-700 @ 1120 in an abit vh6t mobo that seems very stable @ 1.8v. That is the highest bios setting without doing a vid pin mod. I belive the st6 is pretty much the same board except the vh6t uses a Via chip set. I originaly bought it to put my Cely 1.3a in but so far the cely has not oc,d very well in that mobo so I stuck my old p3-700 in and just thought I,d try it out and it was so successful I stuck my cely 1.3a back in my old MSi mobo @ 1456. Now I have two pretty good computers to play with although I still wish I had bought a 1.1a or 1.2a. I will probably buy one to compare.
Good luck I hope this is useful info.