You can get 6x bus speed for any standard AMD K6-2 over 350 by setting the multiplier to 2x and the processor type to P55C. While BIOS might say 133 (2x66), the processor understands it as 400 (6x66) and effectively becomes an overdrive. The best voltage setting is 2.2v, but the standard 2.8v Intel MMX core voltage is tolerated if lower settings are unavailable. If you can adjust the bus from 66 to 75 you can get the K6-2 to 450, and to 500 at 83. To verify your results you can use wcpuid or other testing programs, but it does work, and it actually works better than other boards that were made for the K6-2 because the Intel chipset has fewer compatability/stability issues. The processor can be had for under $50.
I have sold systems with this settup and have had no warrantee returns. If you feel uncomfortable with these voltage settings, you can get a processor with resistors added from www.evertech.com for a little more.
Suicide is painless...........