Go to C:\Program Files (x86)\Steam\steamapps\common\Quake Live\XXXYYY\baseq3 where XXXYYY is your profile generated number.

Create an autoexec.cfg file and put this command inside :
seta com_idleSleep "0"

This command will prevent the CPU from going in sleep state inbetween each rendered frames. Without this command even with a very good PC I had drops on maps using transparent shaders (e.g. Asylum, Quarantine) and or maps with a lot of players.

Add to the autoexec.cfg file this command :
seta com_maxFPS "250"

The game engine can only render a frame rate that is a round number divider of 1000. You can't use anything else, it will always go with the closest value to the rounded divider of 1000.
Here is the list :
1000 / 4 = 250 fps (this is the maximum).
1000 / 5 = 200 fps
1000 / 6 = 166.6 fps (will fluctuate)
1000 / 7 = 142.8 fps (will fluctuate)
1000 / 8 = 125 fps (default)
It can go lower than 125 fps.

As an exemple, if you set your com_maxFPS to 240 it will render 250 fps.