Good question! Apparently, BOOST does not increase frame rate for you.
The other useful things it still does is decreasing lag and making mouse control better. So, try playing with and without BOOST (you can toggle it with F10) and see how it feels. Some people are very sensitive to such things, some are not. If you do not feel more comfortable with BOOST, don't use it!
About increasing CPU temperature - it differs from computer to computer. When this is important: (1) if you are playing on battery: the battery will last less time; or (2) when CPU is getting so hot that protective measures kick in and decrease its performance: you will get significantly lower frame rate, this should be clearly visible.
Should you use Chill? Only if you have problems like (1) or (2).