Important to note about these Cyrix 5x86 CPUs is that they are really, really configurable. I'd take a look around at some guides out there regarding CPU register settings. It may seem a little intimidating at first, but with utilities like IBMM9.exe, it's not too bad. There's lots of flexibility in the 5x86 (depending on the motherboard you're using, as well), and it can range from fast, to really, really fast.
As Timo W. mentioned, the turbo button is 100% mainboard related, but there are not only cache control apps for Cyrix 5x86s but also things like SETMUL and CTCHIP allow you to change the CPU multiplier in software and slow the system down a good bit.