I got my AMD K6-2 300 to 375 (68Mhz*5.5) at 2.3 volts Stable!. For some reason I could overclock more when I lowered the bus speed and increased the multiplier. I have a friend who also has a K6-300 and he can't go higher than 366 without random crashes in windows regardless of how the Bus Speed is set.
Played around with all settings up to 400, but it only runs stable at 300 (100x3.5 @ 2.3volts) Any faster, no matter what the voltage, and it isn't stable.
Just try and see. Some people have taken the 300 all the way up to 400 easily, sometimes without even having to change the voltage! Lucky B*****d's
But I'm happy with mine at 350
Keep On Rockin' 'n' Overclockin' ;-)