Now that the new 27-inch iMac is available for purchase I've been receiving requests from people who are wondering if they should purchase a 27-inch iMac, or whether a 21.5-inch iMac is fast enough for their needs.
To help answer that question I've collected Geekbench results from the Geekbench Browser for both the 27-inch iMac and the 21.5-inch iMac. If you're not familiar with Geekbench, it is a cross-platform benchmark that measures processor and memory performance. Higher Geekbench scores are better.
If you're curious how your Mac (or PC!) compares to the new iMacs you can download Geekbench and find out (it only takes a couple of minutes to run).
iMac Performance (27-inch 2012 and 27-inch 2011)
Before comparing the new 27-inch iMac to the 21.5-inch iMac, I was curious to see how the new 27-inch iMac compared to the old 27-inch iMac. As you can see from the chart, the new 27-inch iMac models are between 13% and 19% faster than last years models (when comparing equivalent models). This increase is thanks to both the new Ivy Bridge processors and, for the mid- and low-end iMac, a slight bump in processor speed.
iMac Performance (27-inch 2012 and 21.5-inch 2012)
Somewhat surprisingly, the new 27-inch iMac models aren't that much faster than the new 21.5-inch iMac models. Only the low-end 27-inch iMac is significantly faster (13%) than the low-end 21.5-inch iMac. The other 27-inch models are only 3-4% faster than the equivalent 21.5-inch models.
Should you get a 21.5-inch iMac or a 27-inch iMac? Unless you're looking at the low-end models, processor performance isn't different enough to recommend one over the other. Which Mac you purchase will come down to personal preferences. Do you want a bigger screen with a more powerful GPU? Or do you want a smaller screen that takes up less space? Either way, regardless of which iMac you choose, you'll be happy with its performance.