K6 update on old motherboard?

[Martin Spang-Thomsen]

I have an A-trend ATC1545 motherboard with the Opti Viper-M chipset, bought
in late 1995, intended for regular ol'Pentiums up to 200MHz. Bios: Award
Software 11/16/95.
I'd like to upgrade it with a K6. A 200MHz K6 (just still available) would
be obvious for 200MHz use, but I suppose I will get a problem since my
motherboard probably supplies just one voltage - 3.3V - which is too much
for the K6/200 core supply. I wonder if it wouldn't work with a 233MHz K6
which will then get 3.3V core voltage against the nominal 3.2V.
Any advice or hints to avoid buying an inappropriate chip would be greatly
appreciated!