This doesn't seem to be a case of Apple choosing slower drives for the high-end model. It's just that this Seagate drive is really fast. It took the Seagate-equipped 2.9GHz iMac 96 seconds to copy a 6GB file from one part of the drive to another, while the WD drive in the 3.2GHz iMac took 146 seconds, the same as the high-end 2011 27-inch iMac.
Since Apple doesn't specify hard drive brands or offer detailed drive specifications beyond capacity and rotational speed, it's not possible to know exactly which drive will arrive in your iMac. When we bought a customized 27-inch iMac with a 3.4GHz Core i7, it shipped with the faster Seagate drive installed as part of its Fusion Drive. It's unfortunate that the slower drive came in our high-end system; Nine of the 15 tests that make up Speedmark 8 were faster on the low-end iMac, with the 2.9GHz iMac's overall Speedmark 8 score 6 percent higher than the 3.2GHz iMac's score. (See our recent 27-inch iMac benchmark article for more detailed performance results.)
Configure-to-order storage options include a 3TB hard drive (an additional $150), a 1TB Fusion Drive ($250), a 3TB Fusion Drive ($400), or 768GB of flash storage (a whopping $1300 premium). We've covered Fusion Drive quite extensively, but in brief, this Apple innovation marries a roomy 1TB or 3TB standard hard drive with 100GB of zippy flash storage. The Fusion Drive looks and acts like a single drive to the end user, but in everyday use, performs like an SSD.
The new, thinner, 27-inch iMacs are striking in terms of their design, but the loss of two convenient features--internal optical drives and built-in FireWire ports--dampens my enthusiasm for the makeover. The new iMac's drastically reduced glare and generous 8GB of RAM are features that benefits every user. Enhanced FaceTime cameras, better sounding speakers, and faster processors sweeten the deal, and the optional Fusion Drive's ability to offer an SSD's speed with a hard drive's capacity is a nothing short of a breakthrough in storage. With only subtle differences in processor and graphics performance between the high and low end models, consider buying the $1799 iMac and putting the savings towards the optional 1TB Fusion Drive. That may offer the best bang for your buck