I don't remember if the I-opener bios supports the Cyrix,
My opinion you would be better off with AMD K6.
The Cyrix 433 (PR) is actually 300mhz clock speed, Also I believe lower FPU. MAY be a waste of time replacing the existing 266MHZ Rise CPU with the Cyrix? I could stand corrected on that. May want to do a search here and on the web
Never really played around with the Cyrix much....It's been said the old Cyrix's make good room heaters!
Their are known problems with Cyrix and Windows ME,