It depends how much RAM you allocate for your graphic card, you can have up to 2048 x 1536 32bit true colour at 75Hz
At 1600 x 1200, you can have as high as 120Hz too
One of my PC is using Intel Extreme Graphic, this is the older one, not the Extreme2 or GMA900. I have hook it up to 21" CRT and 20" LCD that support 1600 x 1200, I can run at 1600 x 1200 @ 85Hz without problem, that's the highest that my CRT can support, but many low to mid range 21" CRT can only do 1600 x 1200 @ 60Hz, therefore the refresh rate is never a problem if you allocate enough RAM for graphic, most of the time it is the monitor that cannot take the high refresh rate, that's why these settings will be hidden, just in case you accidentally set the wrong refresh rate and mess up everything