I have an XFX Radeon HD 5750 and I've overclocked it as follows:
ATI Radeon HD5750 1gb GDDR5: overclocked GPU 830 MHz, Memory 1335 MHz
However, in CCC and in other programs, it says that the GPU Core is 300 mhz and not what I OC'ed it to. I still have ran benchmarks and they've definitely increased from the stock settings.
Any ideas as to why this is? I'm at work right now, but if people need me to post screen shots, I will when I get home. You can also see my system specs in my sig below so that should hopefully give you any info that might help.
300mhz is the idle speed, not the max speed. do you have 2 monitors? usually the idle speed is lower than that. on my 5770 the idle speed is 157mhz, but when you plug in a second monitor, even if you aren't using it, it idles at 400mhz.
if you were to download gpu-z and then run a graphics intense program like 3dmark06, you would see the min/max values of the clock and it would indeed hit the 830mhz you OC'd it to.