How does the performance of the high-end Core i5/Core i7-powered "Late 2009" Aluminum iMac compare to the entry-level "Early 2009/Nehalem" Mac Pro? Is there still a reason to consider a Mac Pro over an iMac?

Please note that all Macs mentioned in this Q&A have been discontinued.

Apple did not release official benchmarks comparing the performance of the high-end iMac "Core i5" 2.66 27-Inch (Late 2009) and the entry-level Mac Pro "Quad Core" 2.66 (Early 2009/Nehalem).

However, third-parties excitedly compared the performance of these systems in a variety of synthetic benchmarks and "real-world" tests.

Compiling Geekbench benchmarks, the now defunct Timon-Royer blog presented that the Core i5 and Core i7 iMac models returned results of 7369 and 9638, respectively, compared to 9910 for the entry-level Mac Pro "Quad Core" 2.66 (Early 2009/Nehalem) configured with a 2.93 GHz processor. This indicates that in Geekbench tests, an upgraded entry-level Mac Pro is roughly 34% faster than the Core i5 iMac, but a mere 3% faster than the Core i7 iMac.

Using its Speedmark 6 benchmark suite, the industry-standard MacWorld reported:

With a Speedmark 6 score of 209, the 2.66 GHz Core i5 iMac is the fastest standard configuration Mac we've ever tested. It was three percent faster overall than the 2.66 GHz Quad-Core Mac Pro, and 1.5 percent faster overall than the 2.26 GHz 8-core Mac Pro. . .

With a Speedmark 6 score of 225, the [US]$2199 Core i7 iMac was nearly 8 percent faster than the Core i5 iMac. The Core i7 was nearly 11 percent faster than the [US]$2499 2.66 GHz Quad-Core Mac Pro and 9 percent faster than the 2.26 GHz 8-Core Mac Pro, which sells for [US]$1100 more.

The always excellent BareFeats ran a series of tests and discovered:

The iMac Core i7 (quad-core) finally gives us an "all in one" Mac that can "run with the big dogs." It is just a few steps behind the 2.93 GHz quad-core Mac Pro. . .

What about the Core i5 iMac? Based on the four CPU intensive apps featured in the graphs, we believe it's well worth paying 10% more for the Core i7 iMac to get 13% to 30% more CPU crunching power.

However, [for 3D graphics] the Mac Pro with a Radeon HD 4870 is 45% to 53% faster than both.

Perhaps in recognition of the narrowing performance "gap" between the "consumer" iMac line and the "professional" entry-level Mac Pro on December 4, 2009, Apple began offering the entry-level Mac Pro with a single 3.33 GHz Quad Core Xeon processor for US$1200 more than the stock configuration and lowered the price of the 2.93 GHz processor upgrade to US$400 as well.

Ultimately, the high-end Core i5 and i7-powered "Late 2009" iMac models considerably raised the bar on the performance provided by a consumer level system and are quite capable of competing with professional systems in many tasks at a significantly lower price. However, for those who need expansion options -- additional internal hard drives and expansion cards -- as well as performance and the option of a "matte" display, the Mac Pro remained the only Apple option.

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