August 29, 2011, 10:42:32 am
M-series cards will obviously never be as fast as "full-size" graphics cards.
Notebookcheck.net have carried out a series of benchmark tests, e.g. 3D Mark 11 etc, just click on the "Show comparison chart" options to compare this card to your 460s:http://www.notebookcheck.net/AMD-Radeon-HD-6970M.43077.0.html
The performance in some benchmark tests seem pretty close to a single 460 GTX...
Also, the 6970M is a bit slower (11-21% depending on the benchmark) than my ATI Radeon HD 5850, and in my experience, fillrate tends to be a problem for cards in this price/performance range. The 'fill rate' describes the amount of pixels that a graphics card can render in a given amount of time. In other words, the higher the screen resolution, the lower your frame rate is going to be, so running complex scenes in Lumion in full screen (2560x1440) on the 27" iMac is going to be tricky, unless you're happy with lower star quality in the editor.
You can of course also run Lumion in lower resolutions (in a window), or reduce the Resolution slider in the Lumion settings menu, but that's not ideal if you're expecting better performance when upgrading to an iMac. For comparison, the ATI Radeon HD 5850 performs at 30-45 fps when I fly around the Alpine Dwelling demo scene in 3-star quality at 1920x1200 (in Build 7).