How much faster are the White iMac "Core 2 Duo" models than the original iMac "Core Duo" systems?

Please note that all models mentioned in this Q&A have been discontinued. The "White" iMac Core 2 Duo systems were replaced by the "Aluminum" iMac Core 2 Duo line.

Apple claims that the "White" iMac Core 2 Duo systems deliver "up to 50 percent faster performance than the previous iMac." Although this is true based on the "SPECint and SPECfp rate tests" that Apple uses, it is not true in real-world application tests.

Review a quick comparison of the different iMac "Core 2 Duo" system specs, and one would notice that the three higher-end models -- the iMac "Core 2 Duo" 2.0 GHz 17-Inch, iMac "Core 2 Duo" 2.16 20-Inch, and iMac "Core 2 Duo" 2.16 24-Inch -- have 4 MB of level 2 cache, twice as much as the replaced "Core Duo" models.

In addition to 4 MB of level 2 cache, the Core 2 Duo processor design is modestly more efficient than the Core Duo processor that it replaced.

You might be interested in reading through the details of both the Core Duo and Core 2 Duo processors from Intel's website, but in particular Intel promotes that the Core 2 Duo offers "wide dynamic execution" that enables "delivery of more instructions per clock cycle to improve execution time and energy efficiency" along with "smart memory access" that optimizes "the use of the available data bandwidth" and a "more efficient cache subsystem" among other improvements.

In a "First Look" that should be read in its entirety for the complete perspective provided by the author, the always reliable MacWorld reports that in real-world application tests:

Comparing the results of the new 2 GHz 17-inch iMac to the old 20-inch 2 GHz model, the iMac with Core 2 Duo processor earned a Speedmark score of 232. That’s a 10 percent improvement on the 210 score turned in by the older system. Likewise, most of the individual application tests run on the new iMac showed gains of 10 to 20 percent over the Core Duo iMac. The 2.16 GHz iMac bested its fellow Core 2 Duo desktop, the 17-inch, 2 GHz model, in all but the iTunes MP3 encode test, where both new systems turned in the same score.

Ultimately, 10 to 20 percent faster may not be quite as high as Apple's grandiose claims, but still substantial nevertheless.