Yeah, I do the same. OS and software installations on the SSD, bulk data on the HDDs. With my main Linux setup I go a little further to push /tmp to tmpfs (RAM) to reduce writes to the SSD and increase performance. Of course, I wouldn't suggest doing that until you have a LOT of RAM. I have 16 GB so I can handle the tmp folder and still have plenty of RAM left. On Windows I'd probably turn off virtual memory on the SSD, but I wouldn't bother doing too much more than that. That will reduce the bulk of the writes. You should be fine.
Disabling C-states and forcing speedstep or any other CPU throttling off will make VERY little difference in actual performance. It's not like a CPU takes 5 seconds to spin up to full speed after resting at a lower clock speed. It happens instantly. All you're doing instead is wasting more power. If you're using software on SSD and data on HDD, you could disable HDD spindown on the hard drive and possibly see some lag reduced, but only when the HDD had gone to sleep. If you get a 5 second lag while you hear the HDD spin up, you'll know.