The hotter a semiconductor device gets (CMOS technolgies) the slower it goes. Take a modern CPU/FPGA to -40C and it speeds up it's timing by 15%. This is basic semiconductor physics and Ohms law.
This does not mean a 15% system increase, the timing from the CPU to the peripherals is 15% quicker. If the peripheral is also cooler, it could run quicker. I design systems to work from -40 to 85C ambient, we know from experience they are quicker at -40 than 25C.
Unless you cool your entire system to below 0 C you will not see a significant speed increase. Surprisingly a number of manufacturers keep the affect of temperature on speed under NDA!
HTH
Ian
