Set agp aperture to 256, that might help.
I replaced the stock cooler on mine because it was too loud, zalman vf700cu lowered temps by about 10c.
That stuttering you're getting may be caused by your Virtual Memory settings being too low. Try increasing that.
There's a heap file command line that you can use in HL2, might work for CS:S.
Taken from
http://www.tweakguides.com/HL2_7.html. There's some other good tweaks there too.
"Similar to the way you can add command variables to the Steam Launch Options, you can also add them to the Half Life 2 startup by editing the desktop icon used to launch the game. If you don't have a desktop icon for Half Life 2, go to Steam>Play Games and right-click on Half Life 2 under 'My Games', then select 'Create desktop shortcut'. Right-click on the desktop icon for Half Life 2 and select Properties. Under the properties, you can enter command variables in the Target box. For example:
"C:\Program Files\Valve\Steam\Steam.exe" -applaunch 220 -heapsize 512000 +map_background none
The above command line will launch Half Life 2 (-applaunch 220) with a memory allocation of around 500MB (-heapsize 512000), and Half Life 2 will start without a 3D background on the main menu (+map_background none). You can add as many variables as will fit in the Target box, simply make sure you put a single space between each command.
Note that unlike entering the commands in the Steam Launch Options box, if you enter them in the desktop icon's Target box they will not apply when you run Half Life 2 from Steam, whereas the Steam Launch Option variables will apply to Half Life 2 even when you launch it from a desktop icon."
-z