Thanks to our member dwd3885, who went to an apple store to get a brand new high end iMac, we have good evidence of the advertised 5750 in the new high end iMac as being mobility 5850. This is neither good or bad news-- but could be considered as better news rather than worse news. The current speculation was an underclocked desktop 5750, which would provide same performance as mobility 5850. dwd3885's system profiler has marked the ati 5750's device id as 0x68a1, and thanks to our member Horus' link, we are able to get a good idea that the 5750 is actually a mobility 5850. Also, due to Hellhammer's great research, this shows the ox68a1 model to be BroadwayPro/LP, which are both mobility 5830 and mobility 5850. Since mobility 5830 can not use GDDR5 memory, the only logical solution would be mobility 5850. Thanks to our member easepease, we now have image confirmation from gpu-z that the gpu in the new high end iMacs is in fact a default-clocked mobility 5850. How does the mobility 5850 compare with the mobility 4850 in the older high end iMac? About the same. Notebookcheck has the mobility 5850 with GDDR5 being at a slight edge over mobility 4850. New iMac users do get some added benefits as well. Raw processing power and memory bandwidth performance are virtually the same, however a bigger memory buffer will help games with running higher textures and detail, especially at such a high resolution. The higher memory buffer will also help memory intensive applications. The mobility 5850 will also consume a good chunk power less than mobility 4850 due to newer technologies and better throttling (39 watts vs 60 watts), so users will experience a cooler iMac. Also considering mobility 5850's relative cool output, it will be quite easy to overclock it closer to mobility 5870 standards, which is basically a slightly higher clocked mobility 5850. This also probably means the advertised HD 5670s in other iMacs are mobilie 57** cards. Some food for thought: Notebook check has the 1gb GDDR5 version of mobility 5850 playing Bad Company 2 at x resolution with ultra settingss rated at 31fps. Notebook check also has the 512mb GDDR3 version of mobility 4850 (but with 575mhz core clock compared to the 500mz in iMac) at 25fps. If the same core were to be underclocked to 500mhz, we could expect around 20-25fps. Comparison of two cards' memory bandwidth performances: mobility 5850: 128bus width/8bytes x 1000mhz sdram clock rate x GDDR5's quad data rate of 4 = 64gbps of memory bandwidth. mobility 4850: 256bus width/8bytes x 850mhz sdram clock rate x GDDR3's double data rate of 2 = 54gbps of memory bandwidth. As you can see, with 15% greater memory bandwidth and a more efficient processing core, the mobility 5850 with GDDR5 memory will perform around 10% greater than mobility 4850. The mobility 5850 is a 10% slower clocked mobility 5870, so users who want the most out of their gpu could safely overclock to mobility 5870 range under windows-- mobility 5870 is 20% more powerful than mobility 4850, according to notebookcheck.