Fastest Core i7 iMac model rated best buy

The report contrasts the performance benchmarks rankings of Cinebench 11 and Geekbench 2 to compare the the $1699 entry level dual core 3.2GHz Core i3 against the midrange $1999 quad core 2.8GHz Core i5 and the high end $2199 quad core 2.93GHz Core i7.

Overall, the performance scores indicate that the Core i5 offers a performance boost up to 41 percent at just 18 percent more cost, while the high end Core i7 is up to 45 percent faster than the Core i5 while being just 10 percent more. It's also 104 percent faster than the Core i3 model while being just 29 percent more expensive.

"Going by the Cinebench rating, you pay $400 for each rating point on the Core i7, you pay $526 for each rating point on the Core i5, and you pay $629 for each rating point on the Core i3," the site noted, concluding, "the top iMac model is the best buy."

Factors influencing performance

The test results reflect numbers published in our review of the new iMac models, which show a marked increase in performance between the Core i3, i5, and i7 processors (below).

The entry level Core i3 CPU design does not support Intel's "Turbo Boost," a feature that enables individual CPU cores to dynamically speed up when only one is being actively used. It does support Hyper Threading however, which enables the dual core chip to act like a virtual quad core when running software that is optimized for multiple cores.

The Quad Core Core i5 and i7 also pack twice as much L3 cache; 8MB, compared to 4MB on the dual core models. All of the machines use a faster new 1333MHz bus for RAM, although in testing, the site reported that using faster RAM only appears to offer a slight advantage up to 3 percent on the new machines.

However, despite the newest 2.93GHz Core i7 model only being clocked 5 percent faster than last fall's Core i7 iMac, the site noted that "the new Mid-2010 iMac Core i7 was 3 to 23 percent faster than the Late 2009 iMac Core i7 in our various CPU intensive tests."

Compared to the mobile Core i7 used in the MacBook Pro, "the new iMac Core i7 is 43 to 120 percent faster running our 'multi-core aware' suite," the site reported.

Additional considerations when upgrading

The site also points out that while some users may decide they have light uses that don't demand top performance, there are good reasons to pay extra to "future proof" for new apps and uses that will end up making the machine useful longer.

It also recommends considering future resale value, where the additional residual value of a higher end model may recover enough to warrant the additional initial cost.