While playing around on the Apple online store tonight, I came across the on oddity with the 27\" iMac. Here's what the high-end Quad Core model looks like:

27\" iMac (Late 2009) with 2.66 Ghz Core i5 CPU, ATI 4850 Graphics

Normally, the price of this iMac wouldn't overlap with any other model in the line. However, if you take the base 27\" iMac (which goes for \$1699), and upgrade the CPU and graphics card, you'll get this:

BTO 27\" iMac (Late 2009) with 3.33 Ghz Core 2 Duo CPU, ATI 4850 Graphics

What's odd about this is that the BTO iMac costs \$50 more than the \$1999 Core i5-based iMac. While I would like to see a benchmark, I'd be surprised if the 3.33 Ghz Core 2 duo iMac outperformed the 2.66 Ghz Core i5. Normally, you'd think that single threaded workloads would do better on the processor with the higher frequency, but in this case the Core i5 has what Intel calls \"turbo boost\". In this mode, if the processor is running a single-threaded workload, it will turn off the other cores, and overclock the remaining core. According to AnandTech, the Intel Core i5 750 can scale up to 3.2 Ghz in turbo boost mode. That, combined with the improvements in the Nehalem microarchitecture means that in this case, the cheaper iMac is likely the better performer.

But hopefully come November, somebody on the Internet will do a bake-off between these two machines, so we can know for sure.

-Andy.