Limit processor speed like in Windows
No. OS X doesn't have a CPU or even GPU throttling lever that users can toggle.

There is a nice app, gfxCardStatus to know which of the two GPU is engaged on Macs that have two options. It also allows pinning to the higher or lower power consumption which might be of use. It's not clear if there is no way to get past the OS to exercise control of the CPU or just that no-one has programmed it yet.