The trick he mentions he used where he issues a floating-point divide for perspective correction followed by integer instructions allegedly killed Cyrix. Carmack figured out for Quake that the original Intel Pentium could execute a floating point divide in parallel with integer instructions and exploited it. Without that trick Quake produced a disappointing frame rate. The Cyrix 686 CPU was generally faster than the Pentium but the FPU didn't work like that which meant it couldn't play Quake very well.