Niege--I believe my K6-233 pulled 24 watts. Not sure, but it rings a bell. If so, if you mobo supports that, it would handle the wattage for the newer.
Lupen--Yes, you can underclock them, or overclock to 75 or 83. They do not have to run at 100. My FIC PA-2012 ran a K6III-350 @ 75mhz (officially unsupported) with 4.5 multiplier = 337 (at 2.1 volt). Also, I've been told in the forum that 2X is remapped to 6X on these cpu.
--Randy