If you don't want to read everything, I marked all the important information in green. So basicly that is all you need to get the final result. Step 1: Simple overclocking The ATI Mobility Radeon HD 5750, wich is used in the previous generation iMac ( 2010 ) is not a ATI Mobility Radeon HD 5750 in reality. Have a look at the official specifications: Pipelines 400 - unified Core Speed 550 MHz Shader Speed 550 MHz Memory Speed 1600 MHz Memory Bus Width 128 Bit Memory Type GDDR5 Max. Amount of Memory 1024 MB Now let's have a look at the real specifications of the GPU in my iMac: Pipelines 800 - unified Core Speed 625 MHz Shader Speed 625 MHz Memory Speed 2000 MHz Memory Bus Width 128 Bit Memory Type GDDR5 Max. Amount of Memory 1024 MB For those of you who have doubts, this is what GPU-Z shows: Now I know what some of you might think. You think that the software misreads the specs of the card. And indeed that's possible. But wait and read further and I will proove that the specifications are correct. Now let's search for a mobile GPU with simular official specifications. You don't have to put to much effort in it, it's the ATI Mobility Radeon HD 5850M. So the GPU, advertised by Apple as the 5750M is actually the 5850M. Why? We'll never know. But that's not important. Continue reading... Now, I don't know if you've taken a look at the official ATI Mobility Radeon HD 5870M, but if not: Pipelines 800 - unified Core Speed 700 MHz Shader Speed 700 MHz Memory Speed 1000 MHz Memory Bus Width 128 Bit Memory Type GDDR5 Max. Amount of Memory 1024 MB Still with me? The 5870M is nothing more then a slightly higher clocked 5850M. So all that is required is a small, free, tool called "MSI Afterburner" wich you can use to overclock the 5850M ( fake 5750 ) to the 5870M. It requires no skill, no voltmodding, etc... And it has a usefull option "Apply Overclocking at system startup". What's so cool about it? Well, since the 6870M is nothing more then an underclocked 5870M ( beleave it or not, the 5870M > 6870M ), you just upgraded your card for free from an ATI 5750M to an ATI 6870M! That's not all, this GPU can easely get overclocked to 725Mhz/1075Mhz, wich results in a card that performs much better then the ATI 6870M/5870M. Now, in order to test the actual performance increase, I ran FurMark and 3DMark11 at 2560x1440 to see how much increase it would have on such an high resolution. Gaming on a lower resolution is perfectly possible, but would result in a more blurry view. In 3DMark11, my score on 2560x1440 went up from 923 to 1033, in other words, the end-result was 11.92% higher. In Furmark, again on resulution 2560x1440, the score went up from 514 to 583. In other words, 13.42% performance increase. For those of you who want to know the performance score if you want to compare your system performance: Step 2: Get rid off the Bootcamp driver, and install the latest one! Apple and Windows Drivers, it just don't matches. AMD sells many more GPU's thanks to Apple, but when it comes to iMac driver support, it's seems that it's not that important for AMD. You've probably noticed by know that by default, you get the ATI 10.4 driver. When you try to update, the software will search for an update, mention that 11.5 is available, download it and install it. Then, when you go check, it's still the same 10.4 driver. So basicly, iMac users are stuck when it comes to upgrading their driver. Follow these simple steps: 1. Uninstall the current ATI driver completely and reboot your iMac. 2. Download the following driver and reboot your iMac: 64bit - 32bit This small driver update from 10.4 to 11.5 will add the following improvements: - GPU acceleration of H.264 video content using Adobe Flash Player 10.1 ( or higher ) - Video De-blocking support ( Reduces blocking artifacts seen in low-bit rate video during playback ) - Mosquito noise reduction ( Reduces mosquito noise seen in highly compressed progressive video, during playback ) - Official support for OpenGL 4.0 and OpenGL 3.3 - Support for OpenGL 4.1 - OpenGL ES 2.0 support - Enhanced Pull-down detection ( The Pull-down detection algorithm has been enhanced for higher visual quality on certain types of video content ) - ATI Radeon GPU acceleration of VLC 1.1.1 ( or higher ) Media Player - Video accleration for HD WMV video content - Enahnced Dynamic Contrast video controls - Enhanced Video Quality default options - Catalyst AI Texture Filtering updates - Tessellation Controls - Morphological Anti-Aliasing support - Stereo 3D gaming support - Performance increase in 3DMark11/Vantage and many games! - A lot more Catalyst Application Profiles - Many bugfixes/resolved stability issues and enhancements for Windows 7! - And a lote more I probably forgot to mention... Now let's open GPU-Z again: Well well well... Our ATI Radeon 5750 magicly becomes the "ATI Mobility Radeon HD 5850"! And for the fun of it, let's run those benchmarks again. In case you have forgotton, the original scores were "923" in 3DMark11, and "514" in Furmark, both tested on resolution 2560x1440. 3DMark11 => 1074! ( = 15,98% increase! ) Furmark => 656! ( = 27.62% increase! ) For those of you who want to know the performance score if you want to compare your system performance: And offcourse, what's really important is the gaming performance. In UT3 the performance boost wasn't very high, but it's an old game and ATI does not add performance inhancements anymore.