When Apple announced new iMacs last month, it included a major step forward amid the subtle-but-welcome refinements in most of the models: the first ever iMac to offer a quad-core processor. The new high-end 27in iMacs are the first to use Intel’s Core i5 and Core i7 quad-core processors, and they were not available at the time of the announcement. But finally, the wait is over, and the Core i5 and Core i7 27in iMacs have arrived – and let us tell you, it was worth the wait.

There are four standard iMac configurations, three of which have 3.06GHz Core 2 Duo processors and were reviewed recently. The fourth standard configuration is a £1,599 model that has the same 27in screen, 1TB hard drive, and 4GB of RAM as the £1,349 27in 3.06GHz Core 2 Duo iMac, but features a more powerful ATI Radeon HD 4850 graphics card with 512MB of GDDR3 memory and Intel’s Core i5 quad-core processor running at 2.66GHz. The Core i5 has 8MB of L3 cache shared among the processing cores.

The Core i5 features a technology Intel calls Turbo Boost. If an application isn’t using every available core, the cores that are idle shut off, and the active cores speed up. According to Apple, this allows the processor to run up to 20 per cent faster under heavy workloads; that translates to 3.2GHz in this iMac.

As an upgrade option to the Core i5 iMac, you can swap in a 2.8GHz Core i7 quad-core processor for £160 more. The Core i7 also features Turbo Boost (for speeds of up to 3.46GHz), and it also has Hyper-Threading technology that can present itself to highly threaded applications as having eight virtual cores.

To see how well the new quad-core iMacs perform, we ran our overall system performance test suite, Speedmark 6, and the results were quite impressive. In fact, with a Speedmark 6 score of 209, the 2.66GHz Core i5 iMac is the fastest standard configuration Mac we’ve ever tested. It was three per cent faster overall than the 2.66GHz Quad-Core Mac Pro, and 1.5 per cent faster overall than the 2.26GHz 8-core Mac Pro.

Comparing the Core i5 iMac’s Speedmark 6 scores to its iMac siblings, the Core i5 iMac was 27 per cent faster overall than the second fastest iMac we’ve tested, the recently released 21.5in 3.06GHz Core 2 Duo iMac with 1TB hard drive and ATI graphics.

Since the Core i5 iMac has the same hard drive as two of the other three new iMacs, we didn’t see a big difference in our file duplication test, and our unzipping test results were pretty flat across the board. However, we did see a 25 per cent improvement in the Core i5 iMac’s Compressor score when compared to the 21.5in 3.06GHz iMac, a 26 per cent increase in Call of Duty frame rates, a whopping 71 per cent improvement in our HandBrake test, an 88 per cent faster performance in our Cinebench multiple CPU test, and the new Core i5 iMac posted a Mathematica score more than twice as high as the 3.06GHz iMac. That’s a lot of performance bang for an extra £160.

Comparing the new Core i5 iMac to the Mac Pro models, we see the speed advantage going the iMac’s way in our Zip, iTunes, iMovie export, Call of Duty frame rates, and Compressor tests. The Mac Pros stood their ground on our HandBrake, iMovie import test, Cinebench CPU test, and Mathematica trials.

Our tests of the built-to-order Core i7 iMac (which, other than the processor, has identical specifications as the stock Core i5 iMac) showed even greater performance prowess. With a Speedmark 6 score of 225, the £1,759 Core i7 iMac was nearly 8 per cent faster than the Core i5 iMac. The Core i7 was nearly 11 per cent faster than the £1,899 2.66GHz Quad-Core Mac Pro and 9 per cent faster than the 2.26GHz 8-Core Mac Pro, which sells for £2,499 (£900 more). In our tests, there were a few tasks where having eight physical processing cores was beneficial, like our Mathematica and Cinebench CPU tests.

The new quad-core iMacs are outwardly identical to the 27in 3.06GHz Core 2 Duo iMac released last month. The quad-core iMacs feature an LED backlit screen covered with glass at a 16:9 aspect ratio, an integrated iSight camera, four USB 2.0 ports, one FireWire 800 port, a Mini DisplayPort, and a new SD memory card slot. In terms of connectivity all new iMacs offer gigabit Ethernet, 802.11n wireless networking, and Bluetooth 2.1 + Enhanced Data Rate. The 27in iMacs ship with a 1TB 7200rpm Serial ATA hard drive, with a 2TB hard drive option available for an extra £200.